CIGRE SC B5 COLLOQUIUM CALGARY Contribution to PS1 – Q#8 What are the issues that are refraining protection engineers from using additional available protection functions ? What is the present practice of utilities when multifunction relays are applied for protecting transformers ? Florin Balasiu, Transelectrica Romania

AT-200 MVA Protections

Transformer Protection Functions Usually the following protection functions are used: 1. Technological protection Buchholz relay main tank and LTC, direct trip, ER in 87T Oil flow relay Pressure relief devices 2. Differential protection 1 Instantaneous differential Percentage restraint differential – second harmonic blocking Thermal overload, without top oil temperature 3. Differential protection 2 4. Distance protection HV (220 kV)- 21, 50/51, 67N, ER, DR 5. Distance protection LV (110 kV) - 21, 50/51, 67N, ER, DR

Transformer Monitoring Monitoring applied to transformers – separate device HV&LV voltages and currents HV&LV windings temperature Core temperature Oil temperature Pumps and fans Online DGA HV&LV bushings LTC monitoring

Transformer Protection Functions Examples of not used protection and monitoring functions : Over-voltage, except some distribution transformers Over-current, except distribution transformers Over-excitation (U/f>) Negative-sequence Restricted earth-fault Measured values, except commissioning and maintenance Circuit breaker contact wear monitoring

Why ? Why not using additional protection and monitoring functions? Tradition on clear separation between protection (protection engineer task) and monitoring (manufacturer task) Some functions included in other devices (measurement, CB monitoring) Doubt on proper setting calculations Complexity of additional settings Too many protection functions could decrease security