| Protection | Details | Relay Type |
| Differential | 1. Unbiased, with series stabilising resistor | CAG 34 FAC 34 |
| 2. Biased differential | DDG 31 | |
| Transverse Differential | For machine with split phase winding | CAG 34 FAC 34 |
| Over current | 1. Inverse time | CDG 31 |
| 2. Inverse time, voltage controlled | CDV 62 | |
| Stator Earth-fault | 1. Inverse time delay for generator earthed through a distribution transformer | VDG 14 |
| 2. For generator earthed through a resistance or solidly earthed and generator is connected to the system via delta-star transformer | CAG 14 | |
| Standby Earth-fault | For generator directly connected to system | CDG 11 |
| Rotor Earth-fault | Instantaneous, generally connected for alarm | VAEM 21 VME |
| Field Failure | To protect against prolonged asynchronous operation. Used in conjunction with a timer and an auxiliary relay | YCGF |
| Instantaneous over voltage | For over voltage protection of generator | VAGM 22 VTIG |
| Time delayed over voltage | For over voltage protection of generator | VDG 11 VTU VAU |
| Negative phase sequence | To detect sustained unbalance condition, relay characteristics to match machine withstand characteristic | CDN CTN |
| Overload | To detect sustained overload of the machine | CTU 12 CTLM 11 |
| Reverse Power | 1. Primary protection against motoring | WCD 11 |
| 2. Protection of diesel generators against motoring where motoring power is relatively high | CCUM WDG | |
| Backup distance | To provide backup protection against uncleared system faults | YCG 15AA+VAA31 +VAT or VTT |
| Forward under power interlock | Interlock against overspeed | WCD 12 |
| Pole slipping | Protection against pole slipping | ZTO 11 |
| Rotor temperature | To monitor rotor high temperature | DZT 4 |
| Protection | Details | Relay Type |
| Differential | Biased, for overall phase and earth fault of the generator and generator-transformer | DTH 31/32 |
| Over current | Inverse time phase and earth fault protection | CDG 31 |
| Restricted earth fault | For earth fault in transformer winding | CAG 14 |
| Standby earth fault | For back-up protection | CDG 11 |
| Overfluxing | For protection of transformer against over excitation | GTT |
| Buchholz | Protection against insipient fault in the transformer | OBGM |
| Winding temperature | Protection, control and indication | TTT & CTTT |
| Protection | Details | Relay Type |
| Differential | Biased, for phase and earth fault protection in the transformer winding | DDT DTH |
| Over current | 1. Non-directional inverse time | CDG |
| 2. Directional, inverse time | CDD | |
| Restricted earth fault | For faults in transformer winding | CAG 14 FAC 14 |
| Backup earth fault | 1. Non-directional inverse time | CDG 11 |
| 2. Directional, inverse time | CDD 21 | |
| Buchholz | For incipient fault in the transformer | OBGM |
| Time delayed earth fault | To protect the neutral earthing resistor and to provide backup protection | CDG 12 |
| Temperature | Protection, control and indication | TTT & CTTT |
| Voltage regulating relay and line drop compensator | For use with ON load tap changers for automatic regulation of voltage | VTJC&CIJC AVE4 & CAD |
| Overfluxing | For protection against over excitation | GTT |
| Protection | Details | Relay Type |
| Differential | Unbiased, over main winding only | CAG 34 FAC 34 |
| Differential | Biased, over all windings | DTH 31 DTH 32 |
| Over current | Inverse time, phase and earth fault protection, non-directional or directional | CDG 31 CDD 21 |
| Restricted earth fault | For earth fault in transformer winding | CAG 14 FAC 14 |
| Buchholz | Protection against incipient faults in transformer | OBGM |
| Winding temperature | Protection, control and indication | TTT & CTTT |
| Voltage regulating relay and line drop compensator | For use with ON load tap changers for automatic regulation of voltage | VTJC&CIJC AVE4 & CAD |
| Overfluxing | For protection against over excitation | GTT |
| Protection | Details | Relay Type |
| Differential | Biased, for phase and earth fault protection in the transformer winding | DDT 32 DTH 31 |
| Over current | Inverse time, phase and earth fault protection without or with high set | CDG 61 CDG 31 |
| Restricted earth fault | For earth fault in transformer winding | CAG 14 FAC 14 |
| Neutral displacement | For detection of earth fault where low voltage system is insulated | VDG 14 |
| Buchholz | Protection against incipient faults in transformer | OBGM |
This is a common error while using ETAP for the first time, blocking out all calculations. Even though you might’ve added many elements to the layout, ETAP requires some elements, like a cable, line or transformer which has a non-zero impedance value. A circuit breaker helps to add more interconnected branches, but won’t solve the issue. If a transformer cannot be included in your diagram, you have to add a new bus and connect it using a short cable (say, 25 sq.mm, 50 m length) as shown below. This may be labeled dummy, if you like, and won’t affect the calculations in any way. This simple trick will save you from unnecessary hold up (about 1 hour, in my case!!)
