Load Break Switch with shunt trip coil

Hi bhavinraval,

U must connect to contact to Shut trip coil via protection device such OC and EF or even emergency stop in some case. I have used this orientention for my 22Kv system (In glass plant which is handle 5Mva) for short while due to some reasons but as long run and safety consideration, LBS (Load Breake Switch) cant handle heavy fault current. VCB still the most suitable device for protection devices.

Regards

thanks for use-full replay.Can u give comparison of LBS & VCB on the basis of cost and size.

I don't know what all the abreviations you guys mentioned me but I do know about shunt trips! We commonly use them to trip a circuit breaker due to relay protection of either primary power sources, transformer or motor protection. What must be noted is that shunt trips require an auxiliary contact to deergize them after tripping or they will burn up! Do not use shunt trips for interlocking as they will get you in trouble! I prefer undervoltage releases.

There are 4 types ( not counting power switching thyristor) of "switches" in MV power supply circuit.

1. Isolator switch, insulated in air,oil or SF6 gas.

2. Contactor , insulated in air or vacuum.

3. Load Break Switch,LBS, insulated in air,oil or SF6 gas.

4. Circuit Breaker ,CB, insulated in oil,vacuum VCB and SF6 gas SF6CB/GIS.

Each type is designed to perform a particular range of duty and purpose.The electrical "strength" or robustness generally increases from iterm 1 to 4.

In reponse to your question,you should use VCB at the main intake station and if you have other down stream distribution substations then you can use load break switches.For larger ring system involving more than 4 or 6 s/s,one or two more VCB s/s to be inserted in the ring ckt.VCB which has a higher KA rating, allows you to equip with CT,PT,O/c E/F IDMT relay,Metering ,Shunt Trip, is about 3 times costlier than LBS.LBS CANNOT be used to trip short circuit current.When that happens,the fault current will be detected by upstream feeder VCB panel and trip safely accordingly.

Regards,

Khor

Dear Khor, first of all thanks for replay. i have not very good idea about LBS. As per IEC standard MV voltage range is 3.6kV to 24kV. If i want to use vacuum contactor / interpretor in 22kV system it is not possible. because such contactor is not available above 6.6kV. Regards your replay related to fault discrimatation, If i you E/F relay to scene e/f and for Short circuit protection i want to use HRC fuse. it is possible? I am also think that i use IDMT relay with protective CT for O/C fault and Short circuit protection, its give trip command to master trip relay(86), contact of 86 open the LBS. This logic is OK or NOT? Secondly i want to know perfect application of LBS in industries even some disadvantage like not able to handle fault current interprettion.

Bhavinraval,

First,please check with your local power supply authority about the requirement of the incoming swichgear that will direcctly receive their 6.6 kv supply.Ask them about the breaking capacity of the switchgears that will be connected to their supply besides,6.6kv,50Hz etc.For example they may demand that you have incomer VCB that is rated for 18.4,20 or 25 KA 3sec.The reason for this is that when there is a serious fault in your installation,your switchgears should be strong enough to withstand the fault current and give them enough time ( they may set their relay to trip within 1.5 sec ) to trip the supply that is sent to your substation.In short,try not to use LBS at this main substation which you up-stream even they no sepecific requirement on this.You do not need to call them each this happens.

For a simple one substation installation, that has one incomming 6.6kv supply and one feeder to one 6.6/0.433kv DYn11,( 1MVA ) transformer,one LV 415V MSB...,You can use one 6.6 or 11kv ( same size and price ) incoming VCB panel,c/w ct,pt,idmt relay for oc & ef,meterings, coupled to another VCB with idmt relays etc or LBS with HRC fuses( NOT relay ) with striker pin type.You can add tripping of feeder on transformer high temperature/pressure on either the feeder VCB or LBS which trip on the normal currents.

Rgards,

Khor.