INSTALL LOADBREAK ELBOW ON XLPE

PRIMARY CABLE

OBJECTIVE

Given all required tools, equipment and supplies you will learn how to install a loadbreak elbow on a length of 25-kV XLPE concentric neutral primary cable. The elbow will be installed to the manufacturer's specifications provided.

INTRODUCTION

You will learn how to make a splice and a termination on high voltage underground cable and you understand the design of the cable. Splices duplicate this design, allowing proper cable operation. In terminating the cable with a stress cone you ensured adequate stress relief and leakage distance. The splice was fully insulated and shielded for direct burial. The stress cone, while partially insulated, still had unshielded insulation with an exposed connector alive at line voltage. Stress cone terminators are used at live front installations, padmount and poletrans transformers, riser poles and various live front switchgear. In this module we will discuss the load break elbow, an insulated termination used on dead front installations.

CLASSES OF ELBOWS

There is a definite trend toward dead front equipment which has no exposed high voltage parts. Cables feeding dead front equipment must be terminated with components providing stress relief and complete insulation. A terminator providing these two functions is the Elbow. Elbows fall into two classes: "non loadbreak", that can only be operated while isolated: "loadbreak ", that can be operated energized and interrupt up to 200 amperes of current. Non-loadbreak elbows, while still in use, are being phased out in preference for the loadbreak type. Any operations of the non-loadbreak type requires the circuit to be isolated involving a power interruption.

The loadbreak elbow is designed for energized operation. It has load interrupting capabilities up to 200 amps. This means it can be

installed or removed using live line tools from energized apparatus, becoming a switch for isolating or sectionalizing equipment or cable. Energized operation of the elbow only takes place after the elbow has been installed as a terminator on the cable. The elbow is not installed on the cable when the cable is alive.

Loadbreak elbows have a ceramic tip on the electrode pin extending beyond the mouth of the elbow. This ceramic tip plays an important role in picking up or breaking load. Non-loadbreak elbows lack this tip and the end of the pin is recessed inside the body of the elbow.

INSTALLING THE ELBOW

You will follow the manufacturer's specifications provided. As with all underground cable work, close attention to specifications, details, cleanliness and good workmanship are a must.

As a matter of fact when you have installed the loadbreak elbow following the manufacturer's specs provided with each elbow, you can install any type of elbow, non-loadbreak, junction ‘T', etc. by simply following the manufacturer's specs supplied with each terminator.

Figure 1

Figure 1, identifies parts of a loadbreak elbow. When using jacketed cable, as you will be using here at the training center, SAP tape and PE (polyethylene or vinyl) tape are installed as shown to provide a water seal between the bottom of the elbow and the cable jacket. You will water seal your elbow after you have installed it following the manufacturer's specifications. As an aid, when performing this step, do not connect the single grounding strand to the elbow grounding eye until the waterproof taping is done. Don't forget however to connect the strand to the grounding eye as the last step.

It describes how a loadbreak elbow accomplishes loadbreak-loadmake operations.

Before you begin to install the loadbreak elbow, there is general information you should know.

Loadbreak elbow connectors are equipped with an integral capacitive test point. This test point can be used to establish whether or not the circuit is energized. The voltage test point is a capacitive device and does not make any direct connection to the conductor. It can only be used with instruments designed for this purpose. Conventional voltage measuring units, voltmeters or phasing sticks will not give any indication because of their low impedance.

Whenever you operate a loadbreak elbow, put yourself in the best possible operating position. This position should let you establish firm footing letting you grasp the clamp stick securely maintaining

positive control over the movement of the elbow before, through, and directly after the operating sequence. If there is question as to the proper operating position, operate the connectors deenergized. Often it makes disconnection easier if you rotate the elbow slightly with the clamp stick breaking the surface friction between the elbow and the bushing before pulling the elbow off.

Whenever you operate loadbreak elbows "alive" wear rubber gloves, flash glasses and use a grip-all clamp stick. Elbows must never be operated energized using only robber gloves regardless of system operating voltage.

If elbows are non-loadbreak or if doubt exists, perform switching to isolate the cable. Non-loadbreak elbows do not have any mechanism for breaking an energized circuit. Unless they are properly installed on the proper bushing they will flash over.

Whenever you tag loadbreak elbows according to the lockout and tagout procedures, the tags should be applied by securing to the elbow's pull ring normally used as a gripping point for a clamp stick when operating the elbow.

PROCEDURE

Read instructions thoroughly and completely prior to beginning

this operation.

STEP 1

a)         For vault-type transformers (submersibles or top bushing), train the cable so it is located in the final assembled position with enough slack to provide adequate clearance and cable slack for operating the elbow with a live line tool for placement on operating accessories.

Note: Cable should extend straight out of the elbow body before making a bend to avoid excessive stress on the elbow.

For padmounted transformers, train the cable so it is located in the final assembled position with a 2" offset to provide

            adequate clearance and cable slack for operating the elbow.

b)  Position the cable with sufficient operating slack and mark the cable even with the center of the transformer-bushing insert. Measure down the cable 11" and remove the jacket and separator tape to this point. Bind off the neutral wires about 2" above the jacket with a wrap of tinned copper wire, unwrap the wires to this point and cable them together leaving one strand for connecting to the elbow grounding eye. Cut the cable 3/4" short from the centerline of the bushing.

Figure 2

STEP 2

Remove insulation shield and cable insulation 1 15/16" from the cable end. Cut squarely. Do not pencil. (Wire brush bare aluminum conductors and immediately insert in conductor contact containing inhibitor.)

STEP 3

Position conductor contact on prepared conductor so the flat contact area faces the brushing plug. Hold the contact barrel against the cable insulation and then crimp the contact. Start crimps at the crimp line mark indicated on the contact barrel and rotate 90 degrees each successive crimp or indent. Carefully wipe excess inhibitor from the outside of the contact and cable insulation. Refer to crimp chart for recommended crimp tool information.

STEP 4

Remove the insulation shield to a point 6 7/8" back from the end of the contact with a straight smooth "squared" cut. Do not cut or nick the insulation.

The 6 7/8" measurement must be accurate and from the End of the crimped connector. This will allow the cable and connector to be inserted to the correct depth inside the elbow. Clean the bare insulation with grit cloth and wipe clean with isopropanol. Wipe towards the semi-con shield. Wrap a layer of vinyl tape around the semi-con shield 1" back from the bare insulation. This will be a guide mark when the elbow is installed on the cable.

STEP 5

Lubricate the cable insulation and inside of the elbow connector housing with the silicone grease supplied (Do not substitute). Do not use more silicone grease than is necessary.

Slide the elbow connector onto the cable with a back and forth twisting motion until it cannot advance any further (the lip of the elbow should be flush with the wrap of tape on the semi-con jacket).

Rotate the connector until it is aligned with the bushing plug.

Remove all tape from cable.

STEP 6

Remove protective cap from of the male contact. Before installing, make sure the Belleville washers are in place. Insert the threaded end of the male contact into the receptacle end of the connector and engage the male contact threads with the conductor contact threads, being sure the threads are properly aligned. Eight to nine half-turns of the male contact can be made using your fingers before it becomes snug in the conductor contact.  A dab of silicone on the threads helps in the mating of the threads.

Caution: If great resistance is encountered in the first half-turn to 1 1/2 turns, do not force. Remove male contact and check threads for possible stripping. If threads are good, reinsert and engage threads being sure they are properly aligned. If threads are stripped, the conductor contact and male contact must be replaced.

Next take the male contact wrench, insert the short end of the wrench into the hole in the male contact and tighten until the wrench bends.

STEP 7

a)         Seal the elbow to cable area with SAP tape (two half lapped layers) and cover with vinyl tape (two half lapped layers) to waterproof the cable jacket

b)         Insert the end of the single strand of neutral wire through the grounding eye and twist to make a small loop, taking care not to damage the eye.

c)         Connect the concentric neutral wires and the grounding eye connection wire to ground using an appropriate connector.

STEP 8

a)         Lubricate the receptacle portion of the elbow connector with the silicone grease supplied. Do not use too much silicone grease because it may force the elbow off the bushing in time. Lubricate the mating bushing only if the transformer is known to be de-energized.

b)         Place the elbow connector on the bushing plug with a fully insulated shotgun stick in accordance with the recommended operating instructions.

INSTALLING STRESS CONES

1.         Glossary

2.         Introduction

3.         Outdoor Application

4.         Installation of a 3M Quick Term II

5.         Elastimold Single-piece Terminator

Creep Distance

Is the distance over the surface of a termination from the line electrode (conductor) to the ground shield.

Example of creep distance:

            Figure 1                                                                                 Figure 2

By installing a modular terminator on the prepared cable, the creep distance is increased from 22.8 cm (9") to 45.7 cm (18").

Figure 3

Figure 6

ii)    use only aluminum oxide abrasive; grit size 120 or smaller or

iii)   be careful not to reduce the cable insulation diameter below  that allowed by the kit.

Figure 9

Figure 10

Figure 11

5.      ELASTIMOLD SINGLE PIECE TERMINATOR

Figure 12