High Voltage(150 kV) Indoor Bus-Bar protection

Website: http://www.facilities.upenn.edu/uop/Div16Electrical.pdf

This is what the University of Pennsylvania have in their Finals tests:

The distribution systems shall be designed so that a high level of reliability is maintained.

A system may include primary and secondary selection with main-tie-main on the primary

(13.2 kV) and main-tie-main on the secondary (480 or 208). Systems shall be equipped with

automatic transfer schemes on both the primary and secondary. Primary main-tie-main

switchgear shall include bus differential protection and shall coordinate with upstream

substation breakers. The design of the distribution system varies with project size and must

be coordinated with the University. The designer is responsible for assessing the needs of

the University and basing the design on such. In general, all buildings will have two (2)

primary (13.2KV) feeds. Where fused primary selector switches are provided on

transformers/substations, non-load break switches shall be provided upstream to allow for

isolation and maintenance of the selector switches without de-energizing the primary service.

In general, all secondary switching devices shall be breaker type. Mains, ties, and 1000

amperes or larger feeder breakers shall be drawout power air circuit breaker type.

Metering shall be provided. Provide each secondary with a panel-mounted

microprocessor-based monitoring device for digital readout of electrical parameters AC

current A, B, C Phases, AC Volts A-B, B-C, C-A "including phase averages "A-N, B-N,

C-N and average phase to N. Real Power (Watts) reactive power (VARS), Apparent

energy (VAHR) for each phase. Real energy (WHR), reactive energy (VARHR),

apparent energy (VAHR) for each phase. Frequency (Hz), Demand (AMPS), system

real power (WATTS), System reactive power (VARS) and system apparent power (VA).

Switchgear General Construction

A. The switchgear enclosure shall be of metal-clad construction as described in ANSI

standards. [In addition, the switchgear shall be Arc Resistant type as described in

ANSI standards.]

B. The switchgear shall be factory assembled into convenient shipping groups and tested

and of a coordinated design so that shipping groups are easily connected together at

the site into a continuous line-up. Necessary connecting materials shall be furnished.

C. The switchgear shall be accessible from all sides. Primary cables connections shall

be made at the top.

D. The switchgear assembly shall consist of one or more vertical sections, each of which

shall have as appropriate for the application:

1. Main bus compartment

2. Primary connection compartment housing cable / bus duct connections,

For a 150kV busbar such busbar protection would be recommended if you have a double busbar system with interconnecting breakers and more than 5 or six outgoing fields. If you're talking about an outdoor switchyard it is mandatory. The point is that distance protections on your outgoing feeders will be primarily be looking at line-side and thus you'd depend on their backup function from the distance protection on the opposed side of the lines that would switch off a few hundreds of milliseconds later (for example 1sec) and in complete imprevisible order, thus exposing your busbars to a higher risk of thermal and mechanical stress related to the short circuit current.

Thanks for the reply. However, I am still not convinced/clear.Would you please clarify with line sketch/cshamatics?

Correct if I am wrong-In my opinion any problem on the Busbars { As we have 150 kV-Double Busbar system-Indoor type with 12 Nos.outgoing feeders and 4-generators feeding ( each generator unit Transfomer 12kV/150kV-star solidly grounded on 150 kV side) with a bus coupler } ,either short Ckt. or Ground,generator breaker will see and trip out. Where differential relay signal will be fed?

Your comments.

Thanks once more

You are making the assumption that all faults will be solid phase to phase or ground faults and that fault currents will be high and fast rising to allow the feeder and generator incomings to see the and discriminate correctly and isolate the faulted section of busbar .If the busbar has many sections , you can have more feeders and generator circuits tripping than is necessary.

With a busbar protection scheme , only the minumum required circuits in the affected zone clears and isolates the fault.

Some faults are on busbar insulators or insulation which do not reach the overcurrent levels etc but can cause significant damamge to busbar, inslators, metal cladding housing the busbar and personal injury. I have seen SF6 gas leakage result in a bus diff protection as a result of a flash to the metalwork.

I have a 33KV, 66KV indoor and 132KV outdoor busbars with many long feeders with distance and other protection and many generators coming into the busbars.

We have seen many operations where the busbar differential operated for minor faults that could have been catastophic.

We have never had false operations of the bus protection since with a well balanced scheme with CTs and wiring sized correctly, both Main and Check zones have to operate to trip a busbar zone.

Hi, just for termination. The mail of djacob is very clear on the subject. So the choice of a busbar protection in bigger installation is justified by 3 reasons:

1) personnel safety

2) protection of the investment, due to more rapid isolation of defaults (do not forget pb that sometimes intervene related to saturation of CT in case of extreme harsh busbar faults, but this is another subject again)

3) Higher availability for the clients (automatic switchover in double busbar systems)

You can find correct busbar protections from most OEM manufacturers as : ABB, Alstom, SIEMENS.

Lots of chance with your topic