What is an Intertrip?
An Intertrip will automatically disconnect a circuit breaker (or) demand from the transmission system in case of a certain condition such as a system malfunction.
This is done to relieve localized network overloads, preserve system stability, control system voltages and/or ensure an immediate restoration of the transmission system.
What is Intertrip in a Transformer?
Intertripping is the controlled use of a circuit breaker to complete the isolation of a circuit (or) part of equipment. In sync with the trip of other circuit breakers. The basic purpose of such schemes is to provide protection for both transformer and equipment’s connected.
Why Intertrip is Necessary?
Intertripping is the controlled tripping of a circuit breaker to complete the isolation of a circuit (or) part of equipment in accordance with the tripping of other circuit breakers.
The primary purpose of such designs is to ensure that protection at both ends of a fault circuit acts to isolate the affected equipment.
It may be employed in the following conditions:
- A feeder with a weak infeed at one end, inadequate to operate the protection for all faults
- Feeder protection for transformer-feeder circuits.
- Faults in the transformer windings may activate transformer protection but not feeder protection.
- Additionally, some earth faults can be undetected due to transformer connections. Faults between the CB & feeder protection CTs which are positioned on the CB’s feeder side.
- Bus-zone protection does not result in fault clearance; the fault is still supplied from the feeder’s remote end, but feeder unit protection may fail if the fault is located outside the protected zone.
- Some distance protection methods employ intertripping to increase fault clearance times for the specific types of faults.
- Intertripping techniques use signals to send a trip command to distant circuit breakers, isolating circuits.
- Intertripping may be employed in high-reliability EHV protection schemes to provide backup to main protections (or) as a backup in the case of a breaker failure.
Types of Intertrip
Intertripping schemes can be classified into 5 types as follows:
1). Direct Tripping
2). Permissive Tripping
3). Blocking Scheme Tripping
4). Operational Intertrip
5). Commercial Intertrip
1). Direct Tripping
Direct tripping applications provide intertrip signals directly to master trip relay.
The receipt of command causes the circuit breaker to operate.
The communication technique must be dependable & secure as any signal detected at the receiving end can lead the circuit to trip.
The communications system must be designed so that interference on communication circuit does not result in false trips.
If a false trip occurs, significant unneeded isolation of the core system may follow, which is generally undesirable & completely unacceptable.
2). Permissive Tripping
A protection relay always monitors permissive trip commands.
The circuit breaker is triggered when the order is received while the protection relay at the receiving end is responding to a system fault.
The communications channel has fewer requirements than direct tripping systems, because receiving an incorrect signal must coincide with the functioning of the receiving end protection (safety) for a trip operation to occur.
The purpose of these tripping is to speed up tripping for any faults that occur within the protected zone.
3). Blocking Scheme Tripping
Blocking scheme tripping are initiated by a protective element that detects faults outside the protected zone.
When an external problem is detected at the local end of a protected circuit, the remote end receives a blocking signal.
Receiving the blocking signal at the remote end prevents the remote end (distance) protection from activating if it detects an external failure.
Loss of communications channel is less significant in this tripping than in others because it does not result in a failure to trip when necessary.
However, the probability of a false trip is higher.
The diagram shows the usual applications of protection signaling & their link to other signaling systems that are routinely used for power system control and management.
However, not all of protection signals indicated will be necessary in any given design.
4). Operational Intertrip
Operational Intertrips are typically installed to provide system security and operational stability. Their primary duty is to protect the power system by automatically disconnecting circuits, feeders (or) generators under particular fault or overload conditions.
Eg: If a fault develops on a transmission line, an operational intertrip can transmit a signal to a remote breaker (or) generator, preventing instability, equipment damage (or) cascading failure.
These systems are quick to respond and are directly connected to the electrical system’s protection relays.
They are not optional; rather, they are required to ensure the grid’s safety and reliability.
5). Commercial Intertrip
Commercial Intertrips are primarily installed to maintain commercial arrangements between a circuit breaker and the distribution system management. They verify that all agreed-upon connection and supply terms are followed.
Eg: A circuit breaker connected to a distribution network may be required to disconnect immediately if a specific transmission line trips, in order to minimize reverse power flow, overloading (or) violating grid codes.
Unlike operational intertrips, they are required for commercial, regulatory (or) professional reasons rather than for the technical safety of the overall system.
How do you stop Electrical Tripping?
Electrical overload is the leading cause of circuit breaker trips. Limit the number of devices connected to the same circuit in order to prevent tripping the breaker.
It could require relocating a few appliances (or) devices to another circuit (or) simply disconnecting devices from this breaker.