INSTALL A SPAN OF TRIPLEX AND CONNECT ENERGIZED

OBJECTIVE

You will learn how to run, sag, and deadend a span of triplex and tap it into the existing energized bus. You will then learn how to disconnect and lower the triplex to the ground.

INTRODUCTION

Installing triplex to serve either an overhead service or an underground service via a dip pole is among one of the first jobs you may perform as a lineperson.  This module will deal only with the final deadending of the span of triplex and its connections to the energized secondary at the bus end.

When you are pulling conductors in the vicinity of energized apparatus, special care must be taken to avoid any potential hazards. You must keep conductor tails under control at all times and you must select your hoisting equipment attachment points with care. Ensure they do not contact energized primary or secondary apparatus.  Handline hooks or blocks carelessly connected to a secondary spool rack may become live if insulation has deteriorated and the live conductor is exposed.

Care must so be exercised when installing or removing preforms around live conductors.

When connecting service wires, the wires connect in the following sequence:

            Neutral first                          Live legs last

When disconnecting service wires, the wires are disconnected in the following sequence:

            Live legs first                       Neutral last

These sequences will prevent damage to customer equipment that is operating at the time of connection or disconnection. New models of solid-state equipment (televisions, VCRs, etc.) require some circuitry to function whether turned on or off.

When making taps to energized bus, care must be taken to avoid shorting the conductors with the press tool. Extra care must be taken when clearances are limited (i.e., connecting into spun bus mid-span or connecting into open wire bus).

You will make your connections using squeeze on all three wires. The open wire bus is size 1/0 poly covered aluiminum. The triplex is #1/0.

Note:  When you have tapped in the triplex service wires to the existing bus, the job is complete.  

PROCEDURE FOR NEW INSTALLATION

The span of triplex has already been deadended at the house riser. The connections have been made at the service end, the meter is removed, and the service is ready to be energized.

Proceed as follows:

-     ascend pole and hang the hand line around the pole at the neutral level

-     cover any exposed energized conductors (primary or secondary) that may present a hazard

-     frame the pole with the required hardware for deadending the triplex including the preform deadend

-     install the rope blocks or hoist and grip on the pole in preparation for tensioning the triplex

Note:        If rope blocks are used, install the "C" hook of the blocks into the rack where the neutral will deadend.

Extra care must be taken to avoid contacting the live secondary bus when a hot hoist is used.

-     pull slack out of the span of triplex on the ground and cut off the excess tails, leaving enough to make the connection aloft

-     attach the running handline to the triplex using a conductor grip installed to remove the majority of the sag when the triplex is raised.

Note:        If the grip is installed approximately 5' out from the base of the pole when the triplex is held under tension, it will remove the majority of the sag and allow easy attachment of the tensioning equipment by the lineperson aloft.

-     pull the triplex aloft using caution as it approaches the bus area so the lineperson can control the conductor

-     deadend the neutral to the rack ensuring the tail of the bare neutral conductor is controlled

-     remove the handline and grip used to raise the triplex

-     shape, trim and connect the neutral connector

-     shape one leg of the triplex to the top live leg of the bus, cut to length and mark the location on the bus

-     prepare your connector and place in a readily accessible Iocation (a nut bag works well).

-           remove insulation from the triplex conductor tail first.

-           install the connector on the bus, place the triplex tail into the bottom of the "C",  

-           install the press tool, guard against contacting the bare neutral with the press

-           cover the connector with tape or cover of the correct size

-           repeat this procedure for the bottom leg of the bus and the remaining triplex conductor

NOTE:      If a connection is made between a Copper and Aluminum conductor, always place the aluminum above copper. Do this to delay the oxidation process.

METERING HAZARDS

You will identify metering hazards for single-phase and three-phase installations in the following:

            Instrument Transformers

            Meter change – single- and three-phase

            Self-contained and transformer type

            Point-to-point diagram

MATERIAL AND EQUIPMENT

            Sample          – Single-phase Meters

                                    - Three-phase Meters

                                    - Self-contained

                                    - Transformer Type

                                    - C.T.'s and P.T.'s

                                    - Point-to-Point Diagrams

METERING HAZARDS

Your work as a lineman often involves the installation of transformers and secondary service wires to supply power to customers. Depending on the service size and secondary voltage, a variety of energy meters are installed to record power consumption. Most metering, with the exception of single-phase three-wire self-contained meters are looked after by the metering department or metering contractors. You may, however, assist these people during the installation of a service or deal with metering components on a trouble call.

To give you information to work with around metering installations and the hazards associated with them, this module will briefly look at instrument transformers and their connection to three phase services.

General Purpose of Instrument Transformers

Direct measurement of high voltage and heavy currents would involve large and expensive instruments and relays in a wide variety of designs. The instrument transformer provides a means of changing the magnitude and quantity of voltage and current being measured so that relatively small and less expensive instruments of standard design can be used. They also protect personnel, the measuring devices, and the control equipment from the danger of high voltage by providing insulation between the primary and secondary circuits, thus resulting in increased safety and convenience. In addition, they also make it possible to locate instruments at a considerable distance from the main circuit, using small secondary wiring to remote panels.

There are two kinds of instrument transformers: one operates as a function of voltage called a voltage transformer, symbol V.T.; the other operates as a function of amperage called a current transformer, symbol C.T. These instrument transformers are step-down transformers, that steps the voltage or the amperage down to an acceptable or workable value.

From our previous studies we know that:

           Voltmeters      - have a high resistance, potential coil;

-  Are connected across or in parallel with a circuit;

                 -  Are voltage rated;

                -  Can be safely used within their voltage rating.

           Ammeters  -  Have low resistance, current coils;

                             -  (Direct connected) are connected into or in series with a load;

                             -  All of the circuit current will flow through the low resistance current coil;

                            -  Are amperage rated;

                            -  Can be safely used within their current rating and voltage rating.

VOLTAGE TRANSFORMERS

We cannot use a V/M, rated at 750 V across a primary line of 2400, 4800, 7200, 14,400 or 16,000 V to neutral. But primary voltage can be determined as follows:

            -        Know the nominal system voltage phase to neutral i.e. 2400 V, 4800 V, 7200 V, 14,400 V or 16,000 V.

            -        Take a voltage reading on the low voltage side of an unloaded distribution transformer (no connected secondary load);

            -        Multiply V/M reading by the transformer ratio.

Example:   Nominal Phase to Neutral Primary Voltage = 4800 V. Nominal Phase to Phase Secondary Voltage = 240 V.

            Transformer voltage ratio = Prim. V. = 4800

                                                           Sec. V.     240

                                                        =   20  = 20:1 V. Ratio

                                                              1

This means for every 20 volts in the primary we have I volt in the secondary. This ignores transformer losses that are very small.

A VIM reading of 234 V means we have 234 x 20 = 4680 V in the primary line.

SUMMARY

The unloaded transformer was a voltage step-down transformer that stepped the voltage down at a given ratio to a workable or usable level.

The distribution transformer acted as an V.T. instrument, stepping the voltage down to a measurable level.

V.T.  used in metering could have ratings as follows:

 

They may also be rated to step down primary voltages to 120 V for metering.

The ‘ratio" identifies the multiplier required to determine the line voltage.

Remember V.T. is step the voltage down to a workable and measurable level.

CURRENT TRANSFORMERS

The current transformer or CT. is a device to step the current down to an acceptable or workable level.

Remember that current coils have very low resistance or equivalent to a dead short.

The low amperage side of a C.T. is usually rated at S A. full load (dead short).

C.T.'s are voltage rated so they can be properly insulated to prevent injury to personnel or equipment.

C.T. instrument transformers used in single-phase metering could have ratings as follows:

 


Your meter would only see a maximum of 5A full line current you would multiply the C.T. ratio.

Example:   Using 240 to S instrument current transformer to measure the following currents, an ammeter would indicate the following:

                     Load current 200 A meter; would indicate 4 A.

                     Load current 150 A meter; would indicate 3 A.

                     Load current 100 A meter; would indicate 2 A.

The ratio of an instrument current transformer will vary depending on the maximum line current it is expected to carry.

GROUNDING OF CURRENT TRANSFORMERS

Secondary Winding

All current transformers should have their secondary windings grounded in service because a high voltage may develop in the secondary winding. The grounded secondary winding also protects personnel if there is a breakdown of insulation between primary and secondary windings.

Open Circuited Secondaries

The secondary circuit of a current transformer should never be open circuited when there is current flowing in the primary winding. Under such a condition, the primary current becomes an exciting current that will cause a high voltage to be induced in the secondary winding. The value of the induced voltage could rise to equal the voltage drop across the primary multiplied by the number of turns in the secondary (volts per turn primary equals volts per turn secondary). It is recognized that certain physical limitations would stop the induced voltage reaching its theoretical value, but the voltage will be sufficient to puncture the insulation or give a dangerous shock to anyone in contact with it. Therefore, those working with current transformers should always make certain that the secondary winding circuit is closed. For the protection of workers, a small short—circuiting switch is located on current transformers at the secondary terminals.

Application of Current Transformers

Figure 1 shows a current transformer used to transform a high current to a value that can be measured on a 5 A meter. The ratio of the current transformer is given as 400/5 A and there are 300 A flowing in the line.  What will the meter read? The solution is as follows:

When 400 flow in the primary of the current transformer, 5 A flow in the secondary.

When 300 A flow in the primary of the current transformer, 300/400 x 5 = 3.75 A flow in the secondary. Therefore, the ammeter will read 3.75 A.

Figure 1

Operating Characteristics of:

V.T,'s - are insulated and rated to handle a specified voltage. The full line voltage is applied through a high resistant potential coil similar to a voltmeter. V.T.'s are connected across or in parallel with the service. V.T.'s step the voltage down to a desired level at a definite ratio (multiplier). Since V.T.'s are a function of voltage with high resistance coils there is only minimum current flow. These devices will not be worked on while energized.

C.T.'s - are insulated and rated for specific voltage and they are also designed to carry a specified maximum amount of current similar to an amp meter. Since C,T.'s are connected in series with the load they must carry full line current through a very low resistance.

These devices while stepping the current down could step the voltage up by the same ratio as the current is stepped down. Large secondary voltage or potential difference can only occur if the secondary becomes open circuited. For this reason C.T.'s have shorting bars built into the secondaries for your protection.

The secondary current must always have a completed path (anytime they are energized) from X1 to X2 through:

             1)        The shorting bars (low resistance)

            2)         The current coils of a meter (low resistance).

C.T.'s are designed and built to operate with a maximum current flow of 5 A.        through the shorting device or current coils.

WARNING: You will never open or cause to be open the secondary I circuit of any C.T. while it is energized.

POLARITY

Where C.T. and V.T. instrument transformers are used with instruments or relays which rely not only on magnitude, but also on phase position, polarity is of importance. Polarity is indicated by marking one primary and one secondary terminal as shown in Figure 2. By definition, when current is flowing toward the marked HV primary terminal, it is flowing away from the transformer in the marked secondary lead. This marking corresponds to H1, X1 used on single-phase power transformers.

Figure 2

 


Arrows Indicate Direction of

Instantaneous Current Flow.

Remember:

           V.T.  -  step voltage down

                     -  ratio becomes a multiplier of the meter

                     -  the white dots indicate direction of instantaneous current flow in and out of the H and X terminals

                     -  full line voltage appears across the high voltage side

                     -  They are not to be worked on while energized

            C.T. - Step current down (5 A)

                     -  Ratio becomes a multiplier of the meter

                     -  The white dots indicate direction of instantaneous
                        current flow in and out of the H and X terminals

                     -  Dangerous voltages could appear if the shorting bars are not used when opening the secondaries

                     -  Shorting bars will be used before opening secondaries

                     -  Full line current is handled by this device

TRANSFORMER-TYPE, SINGLE-PHASE WATTHOUR METERS

Transformer-type watthour meters are designed to be used with instrument transformers.

Normally transformer-type meters are clearly marked on the face or the nameplate: "TRANS. TYPE".

The "transformer-type" meters have separate terminals for the connection of the meter's voltage coil.

High Current Loads

When the load on a circuit is too heavy for the capacity of "self-contained" meters (under present conditions this would be over 200 A, for some meters), current-transformers are used to reduce the load current proportionately so that it can be metered with standard rated meters.

General Construction

It is to be noted that the general construction of the transformer-type watthour meters (A-base and S-base) are similar in outward appearance to the "self-contained" units previously described in Level I. Their difference is in their voltage ratings (usually 120 to 240 V), and in their current rating, which is usually .12-10 A.

Current Rating

This nominal rating of .12-10 A is used in conjunction with current transformers of various ratios whose standard secondary rating is 5 A.

 Internal Connections - Comparison

Another distinction in construction between the self-contained and the transformer-type units is the difference in their internal connections. The two-wire and three-wire self-contained units have their voltage coils terminating at the two left-side terminals (front-view of meter), as illustrated in Figures 3 and 4; while the voltage coil of the transformer-type terminates at the two middle terminals (Figure 5).

    Figure 3                               Figure 4                          Figure 5

   Two-Wire                          Three-Wire                        Two-Wire

Self-Contained                 Self-Contained           Transformer-Type

Bottom-Connected (A-base) Transformer-Type Single-Phase Watthour

Meter

Figure 6 illustrates to measure a 120/240 transformer.a bottom-connected transformer-type meter connected V single phase load using a 200:5 A current transformer.

 

  


Installation Checks for Single-Phase Kilowatthour Hour Meters

The intent of these tests is the protection of the workman against the possible "hazard" of installing a meter when the circuit is faulted, thus creating a dangerous situation.

Note: The danger arises if a meter is installed in a meter base with the "load" side faulted, either short-circuited, grounded or live from back feed. This causes the current coils to overheat and burn out. This burn out and resultant flash can cause the meter glass to shatter.

The risk of an injury to a workman installing a socket-type watthour meter can be minimized by performing simple tests prior to installing the meter.

Visual Check:

Visually check: - Wire size, big enough to handle load current or just 5 A (#12)?

            -           Wire, color coded.

            -           Any C.T. or V.1. installed?

            -           Is there a jumper between left-hand terminals?

Mechanical Check:

Tighten terminal connections, preferably before service is energized. If service is energized, use caution and an approved screwdriver.

Voltmeter Checks - Self-Contained

These checks must be sequential.

The line side will be made alive by the hydro transformer. The procedure for livening up a 120/240 volt service is to connect the neutral first, then the live leads. To disconnect a live service, disconnect the live leads first, then the neutral last.

 

 

Voltmeter Checks Transformer -Type Base

The "visual" and "mechanical" checks are very important and should be completed before making the voltmeter checks.

Figure 11

Visual Checks:

            -        Wire size and color code,

            -        The presence of C.T. and possibly V.1.,

            -        The shorting jumper in place between 1 and 3.

Review and compare the installation checks for self-contained and transformer-type meter bases.

Ask the foreman to monitor your practice of the various installation checks.

Self Contained Three-Phase Meters

Most self contained three-phase meters are the socket base type. If you are replacing one of these make sure it is the same type (check model code and wiring diagram on the faceplate).

Do not change one of these meters under heavy load, it is safer to open the main disconnect. It may be difficult to determine how much load the circuit is carrying, of current is flowing, but a rapidly turning disk is an indication, a lot

Some sockets may have a current bypass switch which routes current around the meter for the purpose of changing it.

Note:  If in doubt, disconnect the customer's load before changing the meter.

If the socket meter operates at 600 volts, it will have a disconnect ahead of the meter. It must be open (meter isolated) before an attempt is made to change the meter. Be sure disconnect is locked open and tagged, if it is not in your immediate area and visible to you.

Be careful when working around a damaged meter, it is probably still energized. When in doubt, isolate the service before removing the meter.

 

Transformer Type - Three-Phase Meters

As mentioned earlier, transformer type meters require instrument transformers for operation. Compared with a single-phase transformer type, the meter secondary leads are size #12 and are solid color, for voltage, striped colors for current. Each phase will have its own color of wire red, blue, yellow. Neutral for white and green for ground.

When any work is to take place at these meter installations you must follow the rules mentioned earlier for work on secondaries of energized instrument transformers.

If you are involved in a meter change, be sure you have the same type and rating of meter as the one to be changed. Consult the nameplate.

If in doubt, get direction from the Meter Department.

For isolating V.T.'s and short circuiting C.T.'s to a transformer type meter, a test block is used. The wiring diagram for the particular meter is invaluable as a guide to isolating these meters.

The instructor will show you how to disconnect a three-phase transformer type meter from service.

The attached diagrams show wiring schematics for a variety of transformer type and self contained polyphase meters.

Trace current and potential leads from the instrument transformers and primary leads to the meter.

As part of the check out, you will be required to schematically wire a transformer type three—phase meter to demonstrate your understanding and ability to follow a wiring diagram.

 

SUMMARY

Meters

1.        Energy is the product of power and time.
2.        The three kinds of power are ready by:

            i)          Apparent power - KVA/hr meter.
            ii)         Active power       -KW/hr meter.
            iii)        Re-active power - is calculated as Pf and read as a %                         (the meter will usually do this nob).

3.         Blondel's theorem:

If a common potential point is used the number of elements in a meter is one less than the number of wires in the circuit.

4.         1)        The current coil of a meter is always connected in                                        SERIES.

            2)     The potential coil of a meter is connected from
   phase-to-phase, or phase-to-ground, depending on the rating of the meter.

5.         The left hand terminal of a meter is the line side, facing the front of the meter.

    6.        1)     Self-contained meters will handle services up to 600 V and 200 A.

            2)     Transformer type meters are used on services where either the voltage or amperage of the circuit exceeds the capacity of the meter, and instrument transformers are used.

Instrument Transformers

1.         Current transformers:

            i)       Subtractive polarity, Hl and Xl are marked on the transformer.

            ii)      Must be connected in series witt the load,

            iii)     Lowering the CURRENT value increases the potential value and SHORTING BARS are provided. These MUST be used when installing or removing current leads from the secondary side of the C.T.

            iv)     C.T.'s may be BAR types, or DONUT types.

2.         Voltage transformer:

            i)       Subtractive polarity, HI and X1 are marked On the transformer.

            ii)     Are connected in parallel with the load - from phase-to-phase or from phase-to-ground.

            iii)    A suitable ratio must be determined, i.e. to reduce 600 V to 120 V a 5:1 ratio is necessary.

 

  

  

 

       


SINGLE-PHASE METERING

Definition of a C.T.

A current transformer is an electrical device used to reduce high currents to more readily handled lower currents. In the case of metering we use C.T.'s with 5 amps secondaries.

Definition of a P.T.

A potential transformer is an electrical deviceused to reduce similarly high potentials to low potentials. In the case of metering, we use P.T.s with 115 or 120 volt secondaries for the following reasons:

1)         Allows the use of a standard meter.

2)         Allows the meter to be remote from a metal clad switchgear or power transformer.

3)         Saves space.

4)         Also reasons given in definitions,

Polarity Marking

Polarity markings on an instrument transformer indicate the relationship between the primary and secondary terminals,

e.g, in a C.T. if we assume at any given instant that current is entering the marked primary terminal it is leaving the marked secondary terminal. Similarly in a P.T. at any given instant the phase relationship of the voltage at the marked primary terminal is the same as that at the marked secondary terminal.

Reasons for Color Coded Wires

Color-coded wires are used in metering installations to facilitate the checking of connections.

Reasons for C.T. Links and Potential Fuses

Current test links and potential fuses are used in the secondary side of the instrument transformers in order to isolate the meter and to facilitate the changing and checking, under load, the accuracy of the metering equipment. This test block may become obsolete in the near future due to new test facilities which plug into a meter socket and have a position to replug the meter in and a second position housing test links and fuses.

3-Wire Current Transformers

A manufactured 3-wire C.T. is actually two 2-wire C.T.'s with the

secondaries crossed. However, they are not what we know as standard C.T.'s. The secondaries are wound to given 2.5 amps rather than 5 amps. Therefore with full rated current of 400 amps flowing, the meter sees only 5 amps.

Whereas if we used two normal 400/5 amps C.T.'s and crossed the secondaries, the meter would see 10 amps with 400 amp load and the multiplier would be 40 rather than 80 using the manufactured 3-wire C.T.

Donut or Window Type Current Transformer



 


By now you are all likely familiar with this type of C.T. as it is used in central metering systems. This is normally a 2-wire C.T., however, this is with ONE conductor passed through the window or hole of the donut.

The 2-wire ratio is normally stamped or painted on in large letters readily visible from the ground, however, the 3-wire ratio is usually in much smaller print and in the case of one-phase C.M.'s it is the 3-wire ratio we are concerned with.

In the above illustration the multiplier in a C.M. using this C.T. would be 40.

Assume we have only ONE conductor passing through the window carrying 200 amps then 2.5 amps will be flowing in the secondary. In this case we are using the C.T. as a 2-wire and the multiplier would be 80.

Now we run a second conductor through the window in the opposite direction to the first conductor and again have 200 amps flowing through this conductor. We are now using the C.T. as a 3-wire CAT, and the secondary current is 5 amps. Therefore the multiplier is now 40.

Importance of Secondary Path in a Current Transformer

A current transformer in service MUST always have a path for the secondary current to flow. This path can be either through the meter or a short across the secondary terminals of the C.T. or C.T. isolating links. If a path is not provided for the secondary current to flow, a dangerously high potential will develop across the secondary which is harmful to personnel and/or the C.T.

Calculation of Multiplier

The multiplier of a metering installation is arrived at by multiplying the ratio of the C.T.'s and P.T.'s bear to 1 times meter multipliers.

e.g.     C.T.'s 200/5 amps                     P.T.'s 600/120 volts
            meter multiplier of 1

            metering installation multiplier is CTX PTX Meter X

            40 x 5 x  1  = 200

Selecting Correct Equipment and Material

The selection of the correct size of current transformer is very importa t in order to have the demand section of the meter registering in the best scale position and also not to overload the current transformer.

A useful rule of thumb in sizing a current transformer for a single-phase installation is to multiply the expected kW load by 5, e.g. if you expect a demand of 60 kW you would multiply 60 by 5 and choose a 300/5 amp current transformer. You know immediately, since you are utilizing a 5 amp meter, that with a load of 60 kW the demand pointer will read 1000 divisions.

An important point to remember in choosing the C.T. is to allow for some increase in service capacity an still maintain a good scale reading, In the above example you demand scale would read up to 90 kW, however, you would be overloading the current transformer, Therefore if you expected the customer may add another 25 kW you would choose a 400/5 amp C.T. This would give you a demand reading of 750 divisions and allow for the 25 kW expansion without overloading the C.T.

The meter would be a standard 5 amp, 240 volt, 2-wire meter with a multiplier of 1. The type of base, A or 5, would depend on whether the installation was indoors in a cabinet or outdoors. The former case would call for an A base and the later a socket base meter. In the case of the socket base you must be sure the contractor has installed a self-shorting socket meter base.

Color coded wire is always used from the secondary side of the instrument transformer to the test blocks and also from the test blocks to the meter

The lugs of the C.T. should be supplied by the customer and should be the correct size for the conductor used. It is most important, to prevent heating, that these lugs be bolted securely to the primary bars of the C.T. and that the conductor or conductors are securely fastened into the lugs. If parallel conductors are used do not put them both under one lug. A twin lug should be used in this case. Lug that require Allen wrenches to tighten are preferred over lugs that tighten with a screwdriver.

Wiring of Meters Using C.T.'s

We have divided this into three standard types which you will encounter and listed them in the order you are likely to run into them.

1.         Utilizing a 3-wire C.T. and a 2-wire A base meter.

2.         Utilizing a 3-wire C.T. and a 2-wire S base meter mounted on a remote self-shorting socket base.

3.         Utilizing a donut C.T. and a 2—wire S base meter mounted on a remote self-shorting socket base.

Single-Phase Central Metering

To connect a single-phase central metering installation remember that one live leg of the transformer secondary must go through the hole of the donut C.T. in one direction while the other live leg goes through the C.T. in the opposite direction This in effect reduces the multiplier of the current transformer by one-half.

e.g.      if a 400/5 amp donut C.T. is utilized the multiplier is not 80 as it would appear but 40. In a donut type C.T. each conductor that passes through the hole produces 5 amps in the secondary (under full load conditions). We therefore in effect have a 400/10 amp C.T. and a multiplier of 40.

Ratio of Donut or Window C.T.'s

400/5 amps, 3-wire ratio 200 and 200/5

Meter Creep Check or Ground Fault

To determine if a meter is creeping make sure all lights, clocks, and appliances are off. The meter disc should come to a complete stop somewhere in one complete revolution. Often this will be between the painted spot on the disc or anti-creep holes are between the poles of the magnets.

1.        If the meter disc continues to rotate shut off the main switch. If the meter disc stops the meter is not creeping, however, you may have missed shutting off all the load or there may be a ground. Re-check all load disconnected Turn the main switch back on and pull out the branch circuit fuses one at a time until the disc stops. This is the circuit that has a ground This check only tells you if the ground is in between the load side of the meter and the switch controlling the individual lights or appliances and is - useless if the ground is in an appliance itself. You may wish to call in our Inspection Department at this point.

2.        If with the main switch off the meter disc continues to rotate, remove meter and disconnect the load leads from the meter base and replace the meter. If the disc stops the meter is okay but there is a ground between the load side of the meter and the live side of the main switch.

Installation of a Test Meter

On occasion you may decide to utilize a test meter and should therefore know the correct way to install same. The test meter or meter you are using as your standard to measure against is always connected on the line side of the meter in question. This is to ensure that you are metering all the load as it could happen, if you connected the meter in question on the line side and there was a fault within this meter, you test meter would only see the load that came out of the meter in question.

Checking Polarity of a Current Transformer

One method of checking the polarity of a current transformer is to connect the D.C. voltmeter across the secondary terminals noting the terminal the red lead is connected to. Utilizing a common battery source such as a 6-volt lantern battery, connect the negative terminal to one primary terminal of the current transformer. Using a red lead connected to the positive terminal of the battery and observing the voltmeter closely, just touch the other end of the red wire to the remaining primary terminal of the C.T. and immediately remove it.

1.        If the voltmeter reads in an upward or positive direction you may consider the secondary terminal the red lead was connected to as being the "marked' terminal and the primary terminal the red lead was touched to, the "marked" terminal.

2.        If the voltmeter reads downscale, reconnect the black lead to the other primary terminal and again touch the red lead to the remaining primary terminal. The voltmeter will now read upscale and the secondary terminal the red lead is connected to will be the "marked" terminal and the primary terminal the red lead was touched to will be the "marked" terminal.

 

TEN TIPS ON USE OF METERS

1.        Ammeters and current coils are ALWAYS connected in SERIES with the load.

2.        Voltmeters and potential coils are ALWAYS connected in parallel with the load.

3.        ALWAYS disconnect power before opening the circuit to connect or disconnect test loads for measuring current.

4.        ALWAYS be sure the power is off and capacitors are discharged before taking resistance measurements.

5.        ALWAYS check function and range settings before connecting instruments. Ammeters are much more subject to damage than voltmeters.

6.        NEVER connect test loads across a voltage when MULTIMETER function switch is set for measuring current.

7.        NEVER change the range or function switches while instrument leads are connected to the circuit.

8.        ALWAYS start with the highest range, if in doubt,

9.        ALWAYS zero the meter before taking resistance measurements.

10.      ALWAYS make use of theory. Needed measurements may be calculated. Current may be computed after measuring the voltage drop across a resistor of known value, i.e. I = E X R

11.      ALWAYS strive for accuracy in measurements.

            a)      Resistance readings are most accurate in the center of the scale.

            b)      Voltage and current readings are most accurate in the                                       upper third of the scale.

            c)      Remember, a meter draws power from the circuit it is measuring.

            d)      The VTVM is a "MUST" for accurately measuring voltages in high impedance (high resistance) circuits.

  1. ALWAYS store meter in a safe place with function switch set on TRANSIT or AC volts, with range switch on highest voltage range.

METERING SINGLE PHASE SERVICES     

 

OBJECTIVE

You will answer a series of questions regarding the identification

and operation of a variety of single-phase energy meters.

You will then learn how in this module to install an "S" base meter. The installation must be wired correctly and the proper voltage checks done before the meter is installed.

METERING SINGLE PHASE SERVICES

There are 3 basic types of single phase customers. One is a customer with a maximum of 200 A service; the other two are the multi-service customer (i.e., farms) and the 400 A and greater, single service customer. The 200 A maximum customer uses a self-contained meter while the other two require a transformer type meter.

In this module you read about the self-contained and the transformer-type meter. You will look at the 2 types of meter bases; "S-type" and "A-type" and the differences between them. Also, you will read about the different tasks you will perform in the field to correctly install the proper meter for the service the customer has. As well you will read about how to identify the different types of meters required. You will also read about how to do the proper voltage checks before the meter is installed. Let's first look at the two types of meters; the self contained and the transformer type.

SELF CONTAINED METER

A meter is said to be sell-contained when the only path the load current can take from the source to the customer's panel is through the meter. In other words, if the meter was removed, the service is disconnected from the source and the customer would have no power. This is why it is important to open the customer's main disconnect switch at his panel before we remove the meter. Otherwise, the meter will be "breaking" the load and a flash can occur.

Remember: dump the customer's load before you remove the meter.

Let's have a look at the inside of the self contained meter so we better understand how it measures the energy the customer is using. Electrical energy is made up of 2 components: voltage and amperage. If we measure these and keep track of them over a period of time we can calculate how much energy per hour the customer uses. The meter measures volt amperes per hour, in other words, watts per hour (watts - volts x amps).

Now that we know this, it is no surprise to find current and

potential coils located in the self-contained meter.

In a single phase 3-wire self contained meter the current coils are placed in series on each 120 V leg to measure amperes. A potential coil is in parallel between both 120 V legs to measure the voltage (see Figure 1). The potential (voltage) coil has to have a high resistance because it is between the two 120 V legs of the service. If it was a low resistance coil it would produce a dead short between the two 120 V legs of the service. On the other hand the current coils have a very low resistance because all the current and voltage flows through them. If they had a high resistance, they would heat up like a toaster.

Figure 1

Current coils and potential coils used together are often referred to in terms of "elements". Simply stated, one current coil and one potential coil equals one element. Therefore it can be stated that each coil in a meter represents 1/2 an element The self contained meter in Figure 1 is a 1-1/2 element meter (3 coils, 1 potential and 2 current, divided by 2 equals 1-1/2).

REVIEW

-     2 types of single phase meters                     1.        Self-contained

                                                                              2.       Transformer type

-     self contained means all voltage and current flows through the meter

-     open the customer's panel disconnect switch before removing a meter from service or installing a new meter.

-     a meter measures amperage and voltage and relates it to time

-     a self contained meter contains two current coils and one potential coil

-     one current coil plus one potential coil equals one element

TRANSFORMER TYPE METERS

A transformer-type meter doesn't have the customer's load flowing through it like the self-contained meter. The customer's power is not interrupted when the transformer-type meter is removed. The transformer-type meter gets its name from the fact that it uses a transformer to step down the current (and sometimes the voltage) so that the meter can measure it

A service of 800 A and 120/240 V would need to have the current reduced so that a meter could read it. This is done by a current transformer. These come in two types: donut and bar. The bar type is usually found in cabinets or meter bases while the donut type is often found on poles or in pad mount underground transformers.

Current transformers are designed to supply the meter with a maximum of 5 A. So if 800 A is the maximum service size then a current transformer rated at 800:5 would be required for this service. This is determined by your customer service department. The correct current transformer is ordered and given to the line crew that is installing the service. The current transformer has information written on the name plate which must be recorded for the billing department and the Federal Government

Let's look at the inside of the transformer-type meter and compare it to the sell-contained meter. The transformer-type meter has only one current coil and one potential coil. The individual coils are connected between the top and bottom lug on each side of the meter. The current coil is between the lugs on the left side and the potential coil is between the lugs on the right side (when looking at the face of the meter). Have a look at Figure 2.

Figure 2

The potential (voltage) coil in the transformer-type meter for a 120/240 V service is the same size as the potential coil in the self-contained meter for a 120/240 V service. They both are connected between the two 120 V legs of the service. The two current coils in the self-contained meter are replaced by one 10 A (maximum) coil in the transformer-type meter. By comparing the location of the coils in both these meters you can see that these meters are not interchangeable (see Figures 1 and 2).

The hazards produced by interchanging the meters or installing the right type upside down in the transformer type meter base can cause explosive results. Some common failures being the meter burning out and the CM metering harness melting. A bigger hazard being a large flash and an electrical explosion. Knowing how to tell the two meters apart and which one is required is very important So, lets look at identifying them.

At a quick glance both types look very similar (see Figures 3 and 4). They both have four lugs on the back; they both have face plates with four dials on them. One major difference is that transformer-type meters have "transformer type" written on their face plates underneath the dials. Also, the current rating of the meter is different The self-contained meter has a current rating of 60, 100 or 200 A while the transformer type is rated for only 10 A. The "transformer-type" meter is a two wire while the "self-contained" meter is three. Remember read the face plate before you install a meter. The information written there can ensure you get the right meter for the right job.

Figure 3

Figure 4

Meters are the utility's cash register. To verify their accuracy they must be replaced with a new or recently-tested meter on a routine basis. Most utilities replace and reverify their meters on a routine schedule. At this time they are also spot checked by the Government and sealed. The year the meter is tested in on the seal.

During meter change-outs many incidents have occurred due to installing the incorrect replacement meter. The "S Base" style meter whether, a two-wire 120 V, a three-wire 240 V, or a two-­wire 240 V transformer type, all look alike and will fit on the same meter base. It is therefore very important that the worker observe the important information recorded on the meter face plate.

The four most important items to look for when replacing a meter are: Voltage and current ratings, number of wire and whether it is a

transformer type. Installing a meter with any one of these incorrect could prove hazardous to the worker.

Other information found on the face plate of the meter if overlooked, may not prove hazardous to the worker, yet it is very important to your utility for metering and billing purposes. Some of these are: model and serial number, identification (location) number, multiplier, reading, seal date (when last verified) and type.

REVIEW

-           transformer-type meters require external transformer(s) to step current and/or voltage down so it can be metered

-           when the transformer-type meter is removed it does not interrupt the service to the customer

-           current transformers are designed so that only 5 A maximum  flows through the meter

-           transformer-type meters are one element meters. They only contain one current coil and one potential coil

-           self-contained meters and transformer-type meters are not interchangeable

-           the face plates on both types of meters give the information required to identify the meter type

TYPES OF METER BASES

There are two basic types of meter bases; the "S type" and the "A type". The "S type" meter base is a socket type with four jaws. It is the standard, modern meter base type. It has replaced the "A type". The "S type" meter base has the line and load side leads connected to the jaws of the base. This allows the meter to be removed from its socket base by pulling (see Figures 3 and 5).

Figure 5

The "S type" Meter Base

 


The "A type" base is an older style and it has no socket to "plug"

the meter into. The line and load side leads are connected directly to the meter. So to remove a meter from an "A type" base the leads must be disconnected from the meter first and then the meter can be lifted off its "A shaped" hanger bracket.

Figure 6

The "A type" Meter Base

 


INSTALLING "S BASE" SELF-CONTAINED METERS

Procedure

-  inspect meter base

            ensure that it is wired correctly (line/load neutral)

            ensure connections at lugs are tight

-  make service alive to top of meter base

- do meter base checks with voltmeter

            all tests require that the customer's main switch be open

            and should be performed in the order listed below

SOCKET METER BASE CHECKS

120/240 V - Single Phase - Three Wire

Check #1 Line Side (Source Voltage)

 


Check #2 Load Side (Back Feed Voltage)

Note: Voltage readings other than 0 indicate an abnormal condition.

A ohm meter may also be used for checking load (resistance). If you should have continuity between 3 to 4, 3 to n, and 4 to n you should not set meter.

DO NOT install meter until this condition is corrected.

Check #3 Load Side (Phase to Neutral or Ground Fault)

Note:   Voltage readings other than 0 indicate a load side phase to neutral or ground fault.

DO NOT install meter until this condition is correct.

Check #4 Load Side (Phase to Phase Fault)

           

Note:   Voltage readings other than 0 indicate a load side phase to phase fault.

DO NOT install meter until this condition is corrected.

READING KWH >METERS MANUALLY

Since a significant portion of your utility's revenue is derived from energy usage by Retail Customers, correct meter readings are vital to the system. Accurate readings also have a large impact on customer relations and our credibility as a public utility. Once a customer receives one incorrect billing due to an improperly read meter, every bill from then on becomes suspect.

>KWH METERS

These meters register all of the energy, in the form of kilowatt hours (kWh), that a customer uses. Most utilities use meters that have four dials in the register, see Figure 7. You will also see a very small dial on the right hand side of the register. This is the test dial and you will learn its function as we go along.

Figure 7

The hands or pointers on these dials are driven by small gears which in turn are responding to voltage and current which are passing through the meter.

The gears are installed so that the ratio of each dial to the one next to it is 10:1 (right to left). In other words, the dial on the extreme right is the "ones" dial, the next dial to the left is the "tens" dial, the next is the "hundreds" dial and the dial on the extreme left is the "thousands" dial (Figure 8).

Figure 8

Always read a meter from right to left. You will see as we go through this module that this is the most accurate method.

Let's look at one example of a register from a kWh meter and

determine its reading.

Figure 9

The correct reading in our example is 5230. As you can see, the pointer on the right hand dial revolves clockwise. The next one to the left revolves counter-clockwise and so on as you move to the left.

The test dial in our example above has just completed its revolution and has started on its next one. This will verify the right hand dial reads "0".

Because the right hand dial has completed its revolution and is now to the right of "0" the next dial to the left will read "3" rather than

"2".

This is the method you would use to confirm the correct reading on any kWh meter. Remember the test dial, revolving counter­clockwise, will always verify what the right hand "ones" dial reads. Then you can move from right to left.

USE >OF THE TEST DIAL

Often there is confusion when the dial pointers are around the "0" or the "9". Keep in mind that the method we just outlined will apply in these circumstances as well.

Let's look at an example of this type (Figure 10).

Figure 10

Again, the test dial is the key to determining the correct reading.

Because it is just about to complete its revolution, the right hand dial still reads "9". If the test dial had completed its revolution and was on the opposite side of "0", then the right hand dial pointer would read "0".

With the right hand dial not completely finished its revolution and reading "9", the next dial to the left will read "9" as well. The same will apply to the next dial to the left.

The extreme left hand dial will consequently read "0".

Therefore, the correct reading. because of the positioning of the

test dial, is "0999".

Complete the following self check.

SELF CHECK

1.  Ans:  ___________________

2. Ans: __________________

3,         Ans: __________________

4,         Ans: ________________

5,         Ans: ___________________

6.         Ans: _________________

7,         Ans:  __________________

8.                     Ans:                                              __________________

9,         Ans: ___________________

10. Ans: ________________

ANSWERS TO SELF CHECK

1.         0978
2.         1139
3.         5231
4.         5552
5.         7969
6.         1999

7,                     3796

8.         4545

9.         6900
10.       8051

The main intent of this module has been to ensure that you can correctly and safely install or change a single phase self contained "S base" meter.