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CIGRE SC B5 COLLOQUIUM CALGARY Contribution to PS 1 – Q# 8

CIGRE SC B5 COLLOQUIUM CALGARY Contribution to PS 1 – 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 ?.

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CIGRE SC B5 COLLOQUIUM CALGARY Contribution to PS 1 – Q# 8

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  1. 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

  2. AT-200 MVA Protections

  3. 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 Instantaneous differential Percentage restraint differential – second harmonic blocking Thermal overload, without top oil temperature 4. Distance protection HV (220 kV)- 21, 50/51, 67N, ER, DR 5. Distance protection LV (110 kV) - 21, 50/51, 67N, ER, DR

  4. 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

  5. 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

  6. 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

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