Medium Voltage Application Guide
Medium Voltage Application Guide
Medium Voltage Application Guide
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13757.A<br />
13756.A<br />
13756.A<br />
SWITCHGEAR<br />
Differential<br />
In medium voltage installations, differential protection is mainly used on transformers, motors and generators. Line<br />
currents are measured on both sides of the device, to determine the difference between the input and output<br />
currents (individual or 3-phase average). If the difference exceeds a preset limit, this indicates a phase loss or short<br />
circuit fault condition. A trip will occur, isolating the affected electrical device from the rest of the system.<br />
Transformer application<br />
2<br />
CT1<br />
CT2<br />
3 3<br />
1 4<br />
3<br />
HV supply<br />
Transformer<br />
Differential protection device<br />
MV supply<br />
MV motor application<br />
1<br />
CT1<br />
3 2<br />
3<br />
M<br />
CT2<br />
Incoming supply<br />
MV motor<br />
Differential protection device<br />
3<br />
MV generator application<br />
1<br />
CT1<br />
3 2<br />
3<br />
G<br />
CT2<br />
Output supply<br />
MV generator<br />
Differential protection device<br />
3<br />
Bus zone<br />
This protection is used on bus distribution systems. The 3-phase line currents are measured on all feeders<br />
connected to a busbar system. The sum of currents entering should equal the sum of currents leaving the busbar<br />
system. If the difference in individual or 3-phase average currents is not close to zero, a trip will occur.<br />
Bus configurations can be complex, but by using the status information of all the switching devices on a busbar<br />
system, logic within the protection device can selectively isolate the faulty zone.<br />
710-12280-00A <strong>Medium</strong> <strong>Voltage</strong> <strong>Application</strong> <strong>Guide</strong> Page 123
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