Types of Electrical Protection Relays

Definition of Protective Relay

A relay is a programmed gadget that detects a strange state of the electrical circuit and shuts its contacts. These contacts thus close and complete the electrical switch trip curl circuit henceforth making the electrical switch stumbled for separating the defective part of the electrical circuit from the remainder of the sound circuit.

Types of Electrical Protection Relays

Presently we should have a conversation based on certain conditions connected with a defensive relay.

Pickup Level of Actuating Signal:

The benefit of inciting amount (voltage or current) is on the edge above which the transfer starts to be worked.

In the event that the benefit of the activating amount is expanded, the electromagnetic impact of the transfer loop is expanded, or more a specific degree of impelling amount, the moving instrument of the relay begins to move.

Reset Level:

The worth of current or voltage beneath which a relay opens its contacts and comes in its unique position.

Working Time of Relay:

Soon after surpassing the pickup level of impelling amount the moving component (for instance pivoting plate) of the transfer begins moving and it, at last, shuts the relay contacts toward the finish of its excursion. The time which slips by between the moment while activating amount surpasses the pickup worth to the moment when the transfer contacts close.

Reset Time of Relay:

The time which slips by between the moment while the activating amount turns out to be not exactly the reset worth to the moment when the relay contacts return to their not unexpected position.

Reach of Relay:

A distance transfer works at whatever point the distance seen by the hand-off is not exactly the pre-indicated impedance. The activating impedance in the transfer is the capacity of distance in a distance assurance hand-off. This impedance or comparing distance is known as the compass of the transfer.

Power system protection can be classified into various kinds of transfers.

Types of Relays

Sorts of protection relays are primarily founded on their qualities, rationale, inciting boundaries, and activity instruments.

In view of the activity system, protection relays can be sorted as an electromagnetic hand-off, static hand-off, and mechanical hand-off. As a matter of fact, a transfer is only a mix of at least one open or shut contact. These all or a few explicit contacts the transfer significantly alter their state while impelling boundaries are applied to the hand-off. That implies open contacts become endlessly shut contacts become open. In an electromagnetic hand-off, these end and opening of transfer contacts are finished by the electromagnetic activity of a solenoid.

In the mechanical relay, these closing and opening of transfer contacts are finished by mechanical relocation of various stuff level frameworks.

In the static hand-off, it is primarily finished by semiconductor switches like thyristors. In computerized transfer on and off-state can be alluded to as 1 and 0 states.

In light of Characteristic, the security hand-off can be arranged as:

1. Clear time transfers
2. Converse time transfers with clear least time(IDMT)
3. Momentary transfers.
4. IDMT with inst.
5. Ventured trademark.
6. Modified switches.
7. Voltage limitation overcurrent hand-off.

In light of rationale, the security hand-off can be arranged as-

1. Differential.
2. Unbalance.
3. Unbiased relocation.
4. Directional.
5. Limited earth shortcoming.
6. Over fluxing.
7. Distance plans.
8. Transport bar security.
9. Turn around power transfers.
10. Loss of excitation.
11. Negative stage grouping transfers and so on

In view of the inciting boundaries, the security transfer can be classified as-

1. Current transfers.
2. Voltage transfers.
3. Recurrence transfers.
4. Power transfers and so forth

In view of use, the insurance transfer can be ordered as-

1. Primary relay.
2. Backup relay.

Essential transfer or essential insurance hand-off is the main line of force framework assurance through reinforcement hand-off is worked just when essential hand-off neglects to be worked during an issue. Consequently, reinforcement hand-off is slower in real life than an essential hand-off. Any hand-off may neglect to be worked because of any of the accompanying reasons,

1. The protective relay itself is defective.
2. DC Trip voltage supply to the relay is unavailable.
3. The trip lead from the relay panel to the circuit breaker is disconnected.
4. The trip coil in the circuit breaker is disconnected or defective.
5. Current or voltage signals from Current Transformers (CTs) or Potential Transformers (PTs) respectively are unavailable.

As on the grounds that reinforcement relay works just when the essential relay comes up short, the reinforcement security relay ought not to have anything normal with the essential assurance relay.

A few instances of Mechanical Relay are:

1. Thermal
   • OT trip (Oil Temperature Trip)
   • WT trip (Winding Temperature Trip)
   • Bearing temp trip etc.
2. Float type
   • Buchholz
   • OSR
   • PRV
   • Water level Controls etc.
3. Pressure switches.
4. Mechanical interlocks.
5. Pole discrepancy relay.

List Different Protective Relays are utilized for Different Power System Equipment Protection

Presently we should view which different defensive transfers are utilized in various power framework gear security plans.

SL	Voltage Ratio and Capacity of Transformer	Relays on HV Side	Relays on LV Side	Common Relays
1	11/132 KV Generator Transformer	3 nos Non-Directional O/L Relay 1 no Non-Directional E/L Relay and/or standby E/F + REF Relay	– –	Differential Relay or Overall differential Relay Overflux Relay Buchholz Relay OLTC Buchholz Relay PRV Relay OT Trip Relay WT Trip Relay
2	13.8/220 KV 15.75/220 KV 18/400 KV 21/400 KV Generator Transformer	3 nos Non-Directional O/L Relay 1 no Non-Directional E/L Relay and/or standby E/F + REF Relay	– –	Differential Relay or Overall differential Relay Overflux Relay Buchholz Relay OLTC Buchholz Relay PRV Relay OT Trip Relay WT Trip Relay
3	220 /6.6KV Station Transformer	3 nos Non-Directional O/L Relay 1 no Non-Directional E/L Relay and/or standby E/F + REF Relay	3 nos Non-Directional O/L Relay	Differential Relay Overflux Relay Buchholz Relay OLTC Buchholz Relay PRV Relay OT Trip Relay WT Trip Relay
4	Gen-volt/6.6KV UAT	3 nos Non-Directional O/L Relay	3 nos Non-Directional O/L Relay	Differential Relay Overflux Relay Buchholz Relay OLTC Buchholz Relay PRV Relay OT Trip Relay WT Trip Relay
5	132/33/11KV upto 8 MVA	3 nos O/L Relay 1 no E/L Relay	2 nos O/L Relays 1 no E/L Relay	Buchholz Relay OLTC Buchholz Relay PRV Relay OT Trip Relay WT Trip Relay
6	132/33/11KV above 8 MVA & below 31.5 MVA	3 nos O/L Relay 1 no Directional E/L Relay	3 nos O/L Relay 1 no E/L Relay	Differential Relay Buchholz Relay OLTC Buchholz Relay PRV Relay OT Trip Relay WT Trip Relay
7	132/33KV, 31.5 MVA & above	3 nos O/L Relay 1 no Directional E/L Relay	3 nos O/L Relay 1 no E/L Relay	Differential Relay Overflux Relay Buchholz Relay OLTC Buchholz Relay PRV Relay OT Trip Relay WT Trip Relay
8	220/33 KV, 31.5MVA & 50MVA 220/132KV, 100 MVA	3 nos O/L Relay 1 no Directional E/L Relay	3 nos O/L Relay 1 no Directional E/L Relay	Differential Relay Overflux Relay Buchholz Relay OLTC Buchholz Relay PRV Relay OT Trip Relay WT Trip Relay
9	400/220KV 315MVA	3 nos Directional O/L Relay (with dir.highset) 1 no Directional E/L relay. Restricted E/F relay 3 nos Directional O/L Relay for action	3 nos Directional O/L Relay (with dir.highset) 1 no Directional E/L relay. Restricted E/F relay	Differential Relay Overflux Relay Buchholz Relay OLTC Buchholz Relay PRV Relay OT Trip Relay WT Trip Relay Over Load (Alarm) Relay

Focuses to be recollected in regard to assurance of transformers

1. No Buchholz relay for transformers below 500 KVA capacity.
2. Transformers up to 1500 KVA shall have only Horn gap protection
3. Transformers over 1500 KVA and up to 8000 KVA of 33/11KV proportion will have one gathering control breaker on the HV side and individual LV breakers in the event that there is more than one transformer.
4. Transformers over 8000 KVA will have individual HV and LV circuit breakers.
5. The relays shown above will be given on HV and LV.
6. LAs to be given on HV and LV to transformers of all limits and voltage classes.
7. OLTC conflicted security is to be given where the expert devotee plot is in activity.
8. Fans disappointment and siphons disappointment alerts to be associated.
9. Alerts for O.T., W.T., Buchholz (Main tank AND OLTC) ought to be associated.