Transformer Differential Protection Calculations SEL 787

🌐 Course Title: Transformer Differential Protection Calculations SEL 787

🎓 Headline: Setting Calculations of 132/12kV and 20/26 MVA Power Transformers

Course Description:

Greetings, Future Electrical Engineers!

🚀 Functional Scope: Dive into the world of protection systems with our comprehensive course on the SEL-787 Differential Relay. This advanced device is a crucial component in ensuring the safety and reliability of power transformers. With its three differential elements (87R-1, 87R-2, and 87R-3), the SEL-787 employs sophisticated Operate (IOP) and Restraint (IRT) quantities to calculate the relay characteristic.

📈 Understanding the Relay Characteristic: The SEL-787 relay characteristic can be set as either a single-slope, percentage differential characteristic or a dual-slope, variable-percentage differential characteristic. This flexibility allows for tailored protection settings based on specific transformer conditions and operational requirements.

🧮 Setting Calculations: The course will guide you through the essential settings that define the relay characteristic:

• O87P = minimum IOP level required for operation
• SLP1 = initial slope, setting the stage for O87P at
• IRT = O87P • 100/SLP1
• IRS1 = limit of IRT for SLP1 operation; intersection where SLP2 begins
• SLP2 = second slope, ensuring it is greater than or equal to SLP1

📏 Per-Unit Values and TAP Scaling: The SEL-787 uses the transformer's MVA rating as a reference point. TAP scaling converts all secondary currents into per-unit values, making the ampere values dimensionless and ensuring accurate protection settings. The term "TAP" refers to the per-unit value common to both windings, guaranteeing that for full-load conditions, incoming and outgoing currents sum appropriately.

📢 Practical Application: In this course, we will perform detailed setting calculation for a 26MVA transformer with the following specifications:

• Type of cooling: ONAN / ONAF
• Vector Group: Dyn11
• Rated Voltage HV V: 132kV
• Rated Voltage LV V: 12kV
• Full Load current HV A: 87.48 / 113.72 A
• Full Load current LV A: 1004.12 / 1305.35 A
• Rated Power MVA: 20 / 26 MVA
• % impedance at normal tap (12 no.) : 15.35% / 19.95%
• Type of tap changer: On load
• Voltage at maximum tap V: 151800V
• Voltage at minimum tap V: 112200V

📊 Course Outline: We will delve into the core aspects of protection settings calculations for power transformers, including:

✅ Full load amperes ✅ Short circuit MVA ✅ Short circuit current at HV & LV sides ✅ The relationship between short circuit MVA and percentage impedance of the transformer ✅ Magnitude and phase angle error, its compensation ✅ CT (Current Transformer) error and its compensation ✅ Operating and restraining currents ✅ Pickup current calculations ✅ TAPN calculations ✅ Phase angle compensation settings ✅ Slope 1 & 2 calculations ✅ Harmonics blocking calculations

📅 Course Schedule: Through a series of engaging lessons, interactive sessions, and hands-on activities, you'll master the art of differential protection for power transformers. Join us on this electrifying educational journey and become proficient in safeguarding electrical systems!

Best Regards, Your Dedicated Instructor Team at [Course Provider]