Generator Protection Application Guide


This guide was developed to assist in the selection of relays and relay systems to protect a generator. The purpose of each protective element is described and related to one or more power system configurations. A large number of relays and relay systems is available to protect for a wide variety of conditions. These provide protection from damage to the generator or prime mover. They also protect the external power system or the processes it supplies. The basic principles offered here apply equally to individual relays and to multifunction numeric packages. An example of the typical configuration settings for a 2MW diesel genset using the Basler BE1-11g Generator Protection System, is included.

The engineer must balance the expense of applying a particular relay or relay system against the consequences of losing a generator. The total loss of a generator may not be catastrophic if it represents a small percentage of the investment in an installation. However, the impact on service reliability and upset to loads supplied must be considered. Damage to and loss of product in continuous processes can represent the dominating concern rather than the generator unit. Accordingly, there is no standard solution based on the MW rating. However, it is rather expected that a 500 kW, 480 V, standby reciprocating engine has less protection than a 400 MW base load steam turbine unit. A possible common dividing point is that the extra CTs needed for current differential protection are less commonly seen on generators less than 2 MVA, generators rated less than 600 V, and generators that are never paralleled to other generation.

 Fully drawout half rack case
 ES Series Protection Relays
ES-27 Undervoltage Relay on DIN Rail
ES-55 Power Factor Relay

This guide simplifies the process of selecting relays by describing how to protect against each type of external and internal fault or abnormal condition. Then, suggestions are made for what is considered to be minimum protection as a baseline. After establishing the baseline, additional generator protection, as described in the section on Integrated Application Examples, may be added. The subjects covered in the generator protection guide are as follows:

    • Ground Fault (50/51-G/N, 27/59, 59N, 27-3N,87N)
    • Phase Fault (51, 51V, 87)
    • Backup Remote Fault Detection (51V, 21)
    • Reverse Power (32)
    • Loss of Field (40Q and 40Z)
    • Thermal (49RTD)
    • Fuse Loss (60)
    • Overexcitation and Over/Undervoltage (24, 27/59)
    • Inadvertent Energization (50/27)
    • Negative-sequence Current and Voltage (46, 47)
    • Off-Frequency Operation (81O/U/ROC)
    • Sync Check (25) and Auto Synchronizing (25A)
    • Out of Step (78OOS)
    • Selective and Sequential Tripping
    • Integrated Application Examples
    • Application of BE1-11g Multifunction Relay System
    • Typical Settings
    • Basler Electric Products for Protection

Read more with an approved Basler account

See also: