Stability test of transformer

Stability test of transformer

1. Stability Test of Transformer with bus bar differential protection By Santu Mondal Mob-7477471734

2. Differential Protection Primary Injection with 3Phase 415V AC & Calculation CT Selection Stable & Unstable Condition

3. Primary Injection with 3Phase 415V AC & Calculation for 25 MVA, 33 KV / 6.6 KV HV MVA = LV MVA For HV Side 25 * 1000 = 1.732 * 33000 * I (p) Primary FLC = 437.39 Amps For LV Side 25 * 1000 = 1.732 * 6.6 * 1000 * I (s) Secondary FLC = 2186.99 Amps

4. Primary Injection with 3Phase 415V AC & Calculation for 25 MVA, 33 KV / 6.6 KV % Impedance = 12.5 % Imp Voltage % Zv = 33 * 1000 * 12.5 / 100 = 4125V Apply Voltage @ Primary 415 V HV side short circuit Current = [415 * (FLC) ] / % Impedance Is (p) = (415 * 437.39) / 4125 V Is(p) = 44 Amps

5. Primary Injection with 3Phase 415V AC & Calculation for 25 MVA, 33 KV / 6.6 KV Similarly LV Secondary Current = [415 * (FLC) ] / % Impedance I (s) = (415 * 2186.99) / 4125 V I (s) = 220 Amps

6. CT Selection CT Ratio selection should be proper For Ex. 33 / 6.6 KV Ratio is 5. In primary of transformer CT Ratio is 500 / 1, then secondary of transformer CT Ratio must be 2500 / 1.

7. Stable / Unstable Condition

8. RED – 670, Make - ABB Two Nos. (HV Side & LV Side) X – 302 (A - Tx & B - Rx) Terminals for Communication through Fibre Optic Cable. Tx can send Trip / Inter Trip / Local End Current from HV to LV / LV to HV Rx can receive Trip / Inter Trip / Local End Current from HV to LV / LV to HV

9. Busbar Differential Protection Scheme   In early days only conventional over current relays were used for busbar protection . But it is desired that fault in any feeder or transformer connected to the busbar should not disturb busbar system. In viewing of this time setting of busbar protection relays are made lengthy. So when faults occurs on busbar itself, it takes much time to isolate the bus from source which may came much damage in the bus system.In recent days, the second zone distance protection relays on incoming feeder, with operating time of 0.3 to 0.5 seconds have been applied for busbar protection . But this scheme has also a main disadvantage. This scheme of protection can not discriminate the faulty section of the busbar.

10. Busbar Differential Protection Scheme Now days, electrical power system deals with huge amount of power. Hence any interruption in total bus system causes big loss to the company. So it becomes essential to isolate only faulty section of busbar during bus fault. Another drawback of second zone distance protection scheme is that, sometime the clearing time is not short enough to ensure the system stability. To overcome the above mentioned difficulties, differential busbar protection scheme with an operating time less than 0.1 sec., is commonly applied to many SHT bus systems.

11. Bus Bar differential scheme

12. THANK YOU