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Cable accessories: fundamentals of medium-voltage cable accessories

What are cable accessories?

Cable accessories or separable connectors are the current-carrying components that connect apparatus to cable in 15, 25 and 35 kV systems at 200 and 600 amps.

  • 200 A cable accessories: loadbreak separable connectors including elbows, bushing inserts, junctions, feedthroughs, feedthrough inserts, protective caps, grounding elbows, bushing well plugs, elbow arresters and standoff bushings
  • 600 A cable accessories: deadbreak and loadbreak separable connectors including elbows, bushings, load break reducing tap plugs, junctions, grounding elbows, protective caps, elbow arresters and standoff bushings
Loadbreak connectors
 

200 A cable accessories

Ratings information

How much voltage is seen on a capacitive test point?

The voltage seen on a capacitive test point is 10-12% of line-to-ground voltage.

When does a system need to be fully de-energized for switching operations?

With a deadbreak system, switching must be done when the system is fully de-energized. With a loadbreak separable connector, switching operations can be done while energized. Refer to installation and operation instructions for detail.

What is the overload rating on a 200 A loadbreak system?

200 A loadbreak systems are not overload-rated

At what air temperatures are separable connectors designed to run?

Separable connectors are designed for operating temperatures between -40 °F and 149 °F. They are designed to be switched from -4 °F to 149 °F

What is the available fault current on a 200 A loadbreak connector?

When energizing a 200 A loadbreak connector, the available fault current shall not exceed the 10-kA rating of the connector

What color system is used on bushing nosepieces to indicate voltage class?

  • 15 kV is red
  • 25 kV is blue
  • 35 kV large interface is purple

Installation and operation basics

How much torque is needed in order to get a bushing well insert into a bushing well?

In order to get a bushing well insert into a bushing well, 15 ft-lb of torque is needed

Why is the use of a drain wire important?

Drain wires prevent the accumulation of charge on the component shield by draining the charge to ground

What is the purpose of lubricating separable connectors?

Lubrication makes initial installation easier and helps make future operations less forceful

Why is cleanliness so important when involving an external surface?

Leakage current can increase when external surfaces experience conductive contaminants. This can result in an increase in power loss and cause higher operating temperatures

What kind of grease should be used with separable connectors?

A silicone grease designed for use with separable connectors

Why is a tight fit along the mating face important?

A tight fit helps keep moisture out and dielectric strength high

Why is it important to pull elbows fast?

Slow switching speed can result in arcing across the mating contacts and eventually damage the contacts from the ionized gases expelled into the interface. This could affect the connector’s ability to provide a complete electrical path

What affects the life of a loadbreak connector?

Many variables affect the life of connectors including the number of operations, magnitude of current interrupted and phase angle

Why is it important to keep test points capped?

A contaminated test point can erode the surrounding insulation and lead to a connector failure

How many fault close operations can a separable connector perform?

Loadbreak separable connectors are limited to a single fault close event because arcing can vaporize metal from the contact surfaces and erode arc-quenching materials within the conductor

Fused loadbreak elbow connector

When I prep a cable what should I be concerned with?

Cleanliness is paramount. Keep everything clean and make sure cutbacks are within the tolerances stated in the instructions. It is also very important to avoid nicking the conductor, to have a clean semi-con cutback without jagged edges and to repair any nicks to the insulation. Failure to do any of the above-mentioned items will create hot spots and potential future failure points in the system

My cable coming in exceeds your elbows range taking ability. What do I do?

You will need to use a cable splice to downsize the cable

I cracked a probe tip. Do I need a new one?

Yes, if a probe tip is cracked the probe will need to be replaced

There is some carbon build-up on my probe from switching activities. Is that ok?

Yes, carbon build-up is part of the process. Unless the probe tip is excessively galled or pitted, the probe is still fine to be used and switched

Do I need to chamfer the insulation on my elbow?

Chamfering insulation on 200 A elbows can help make installation easier, but does not electrically affect the performance of the elbow

200 A cable installation overview

Partial vacuum and vented inserts

I have vented bushing inserts. Is that enough to prevent partial vacuum flashover?

Vented bushing inserts help prevent partial vacuum flashover, but are not guaranteed to do so. For example, vents can be clogged by grease or vacuum could be maintained slightly longer by off-axis operation

What are contributing factors to partial vacuum flashover?

  • Occurs on 25 kV or 35 kV small interface products
  • Occurs during removal of loadbreak elbows or protective caps from energized bushings
  • Occurs during the first 0.5” of elbow travel
  • Stuck or seized interfaces
  • Temperatures 40 °F or below
  • High altitudes

What happens during a partial vacuum flashover event?

As the elbow begins to be pulled, the elbow cuff seal is maintained and no air enters the interface. As the operator continues to pull the elbow, a vacuum is formed reducing the dielectric strength of air as pressure drops. This results in reduced withstand voltage along the interface, increasing the probability of a flashover to ground

Posi-Break elbow

How can these products help to reduce partial vacuum flashover?

A large component of the likelihood of partial vacuum flashover is the volts available per inch of strike distance. By increasing that distance, the likelihood of incidence is greatly reduced. For example, a standard 25 kV elbow and bushing insert has about 3.2 in. of strike distance. Increasing that to 5.9 in. of strike distance results in a 4.2 kV/in. of strike distance as compared to the 7.8 kV/in. of strike distance in traditional 25 kV elbows.

 

600 A cable accessories

Dead-break elbow T-body

What is the difference between live-front and dead-front connections?

  • Live-front connection has exposed conductors and connectors
  • Dead-front connection is insulated and touch-resistant 

What a 600 A loadbreak system?

600 A loadbreak system allows for the 600 A circuit to be disconnected while energized and provides a visible break for isolating and grounding

How does the loadbreak system break load at 600 A?

The 600 A “C” connector divides the arc voltage in two — resulting in twice the contact separation since the circuit is breaking in two places. This — plus added dielectric features — enable multiple loadbreak operations

What is a 600 A deadbreak connector?

600 A deadbreak connector is a dead-front T-body connector that is mechanically secured to a transformer, switchgear, sectionalizing cabinet or another T-body that can safely be connected and disconnected when the system is deenergized

What are the types of 600 A deadbreak connectors?

  • BOL-T is a T-body connector used to terminate a single cable to a bushing on a transformer, switchgear, sectionalizing cabinet or another BOL-T connector. It utilizes an insulating plug to complete the dead-front connection
  • BT-TAP is a T-body connector with a loadbreak-reducing tap plug “BLRTP” instead of an insulating plug. This allows a 200 A load break elbow or MOV elbow arrester to be connected
  • T-OP II is a T-body connector similar to the BT-TAP but uses a threaded cable connector and stud to provide a more secure mechanical connection 
Cleer 600 A loadbreak connector system

600 A loadbreak connector system overview

600 A cable installation overview

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