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
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