IEC 60255-127 Measuring Relays and Protection Equipment - Part 127: Functional Requirements for Over/Under Voltage Protection

The IEC 60255-127 standard published by the International Electrotechnical Commission (IEC) describes the minimum requirements for over/under voltage relays. This standard includes the specification of the protection function, measurement specifications and time delay specifications.

This standard defines the factors affecting accuracy under steady-state conditions and performance characteristics during dynamic conditions. Test methodologies for verifying performance characteristics are also included in this standard. The over/under voltage functions covered by this standard are as follows:

• Phase undervoltage protection
• positive sequence undervoltage protection
• Phase surge protection
• Residual/zero sequence surge protection
• Negative sequence/unbalance surge protection

General requirements for measuring relays and protection equipment are contained in the standard IEC 60255-1.

For the purposes of this standard,

• The characteristic quantity expression versus the theoretical curve of time refers to the curve representing the relationship between the theoretically specified operating time and the characteristic quantity.
• The expression curves of the maximum and minimum limits of the operating time refers to the curves of the limiting errors on both sides of the theoretical time versus the characteristic quantity that defines the maximum and minimum operating times corresponding to each value of the characteristic quantity.
• The set value expression of the characteristic quantity refers to the reference value used for the definition of the theoretical curve of the characteristic quantity versus time.
• The expression start time expresses the time interval between the moment when the characteristic amount of the measuring relay in the reset state changes and the moment the start signal is given, under the specified conditions.
• The term operating time expresses the duration of the time interval between the moment when the characteristic quantity of a measuring relay in the reset state changes and the moment the relay operates, under the specified conditions.
• The expression start time expresses the time interval between the moment when the characteristic amount of the measuring relay in the reset state changes and the moment the start signal is given, under the specified conditions.

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