Overview

Dear All,Differential protection is the main protection for any transformer. Differential protection is also called as unit protection scheme, it mean that it will operate in case of in zone fault and at through faults differential protection should not operate. Trainer Introduction:Your trainer brings over 21 years of experience in operation & maintenance, erection, testing, project management, consultancy, supervision, substation automation, SCADA, and commissioning. With a background spanning power plants, high voltage substations, and HVDC installations, he has worked with renowned organizations such as Siemens Saudi Arabia. He has been involved in over 20 high-voltage substation projects across Pakistan and Saudi Arabia.His expertise encompasses a wide range of areas including protection systems, substation automation systems, design, testing, and commissioning of power generation systems, high voltage switchgear, protection relays, and control schemes. He has a proven track record of leading testing and commissioning teams for implementing electrical infrastructure projects for industrial clients, including steel and petrochemical industries.A practical transformers and CTs pose some challenge to Differential Protection. They are as follows:The primary of transformer will carry no load current even when the secondary is open circuited. This will lead to differential current on which the protection scheme should not operate.It is not possible to exactly match the CT ratio as per equation. This would also lead to differential currents under healthy conditions.If the transformer is used with an off nominal tap, then differential currents will arise as the CT ratio calculated for a particular Tap (Nominal Tap) will be different for different Tap, even under healthy conditions.To prevent the Differential Protection scheme from picking up under such conditions, a Percentage Differential Protection scheme is used. It improves security at the cost of sensitivity.In Percentage Differential Protection, we provide a slope feature to the Differential Protection Relay. In modern Numerical Differential protection Relay two slopes are provided.In this course, we will perform the setting calculation of 100MVA transformer with following data:Transformer rating: 100 MVAHV side voltage: 132 kVLV side voltage: 33 kVVector group: YNd1Impedance: 12.5 %HV side current: 437.4 ALV side current: 1749.5 ATap range: ±10%Primary CT ratio: 500/1 ASecondary CT ratio: 1800/1 AFurther we will calculate: Full load amperesShort circuit MVAShort circuit current at HV & LV sidesrelationship between short circuit MVA and percentage impedance of transformerMagnitude and phase angle error and its compensationCT error and its compensationOperating and restraining currentsPickup current calculationsSlope 1 & 2 calculationsHarmonics blocking calculationsThrough fault stability calculationsBest Regards

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