IEC 60255-151 Measuring Relays and Protection Equipment - Part 151: Functional Requirements for Over/Under Current Protection

The IEC 60255-151 standard published by the International Electrotechnical Commission (IEC) describes the minimum requirements for over/under current relays. This standard contains a specification of the protection function, measurement characteristics and time delay characteristics.

The section of the IEC 60255 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 current functions covered by this standard are:

• Instantaneous phase overcurrent protection
• Time-delayed phase overcurrent protection
• Instant earth fault protection
• Time-delayed earth fault protection
• Negative sequence overcurrent or current unbalance protection
• Phase undercurrent protection
• Voltage dependent overcurrent protection

The IEC 60255-151 standard does not cover the thermal electrical relays specified in the IEC 60255-8 standard. 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.
• Setting value of characteristic quantity is the reference value used for the definition of the theoretical curve of the characteristic quantity versus time.
• The threshold value expression of the characteristic quantity denotes the lowest value and the highest value for the dependent time overcurrent and undercurrent relays, respectively, of the input quantity that the relay is guaranteed to operate.
• 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.

Among the numerous test, measurement, analysis and evaluation studies it has given for businesses in various sectors, our organization, with its trained and expert staff and advanced technological equipment, meets the functional requirements for measurement relays and protection equipment, over/under current protection within the scope of IEC 60255-151 standard. It also provides testing services for