M.V & L.V Inter-tripping
Introduction
'Inter-tripping' can be defined as a method in which operation of protection equipment at one end of a circuit enables a signal to be transmitted to trip a circuit breaker at the other end of the circuit.
Inter-tripping is often described as an unconditional-tripping system as a result of this inter-tripping equipment is usually designed with greater security and safeguards than standard protection signaling, to minimise the risk of incorrect tripping.
The Principles
Inter-tripping is therefore very simple but very essential. It can be used in various bespoke applications, however, it is most common within schemes containing M.V and L.V interconnecting circuit breakers. Take the schematic diagram below for example:
As detailed with the dotted line, this emphasises the inter-tripping between the L.V and M.V circuit breakers. Basically whenever one is tripping, under certain conditions, this will also send a trip signal to isolate it's upstream or downstream associated device.
Common applications of such are:
- Restricted Earth Fault - Isolating L.V and M.V circuit breakers
- Manual or electrical opening of the M.V circuit breaker, causing inter-tripping and opening of the L.V circuit breaker
- Differential Protection - Isolating L.V and M.V
- Emergency Power Off (EPO) - Isolating L.V & M.V circuit breakers
- Transformer Fault, such as over temperature - Isolating L.V & M.V circuit breakers
- Opening of transformer doors/transformer access - Isolating L.V & M.V circuit breakers