TRANSFORMER PROTECTION

 INTRODUCTION

 •                          The power transformer is one of the most important links in a power transmission and distribution system.

 •                         It is a highly reliable piece of equipment. This reliability depends on

 •                         adequate design

 •                         careful erection

 •                         proper maintenance

 •                         application of protection system.

PROTECTION EQUIPMENT INCLUDES

 1. Surge diverters

 2. Gas relay: It gives early warning of a slowly developing fault, permitting shutdown and repair before severe damage can occur.

 3.   Electrical relays.

 •                         The choice of suitable protection is also governed by economic considerations.

 Although this factor is not unique to power transformers, it is brought in prominence by the wide range of transformer ratings used( few KVA to several hundreds MVA)

 •                         Only the simplest protection such as fuses can be justified for transformers of lower ratings.

 •                         for large transformers best protection should be provided.

 TYPES OF FAULTS AFFECTING POWER TRANSFORMER

 ·                    THROUGH FAULTS

 a)                         Overload conditions.

 b)                         External short-circuit conditions.

 The transformer must be disconnected when such faults occur only after allowing a predetermined time during which other protective gears should have operated.

 ·                    INTERNAL FAULTS

 The primary protection of a power transformer is intended for conditions which arises as a result of faults inside the protection zone.

 1.                         Phase-to-earth fault or phase- to- phase fault on HV and LV external terminals

 2.                         Phase-to-earth fault or phase-to- phase fault on HV and LV windings.

 3.                         Interturn faults of HV and LV windings.

 4.                         Earth fault on tertiary winding, or short circuit between turns of a tertiary windings.

 5. So called „incipient‟ faults which are initially minor faults, causing gradually developing fault. These types of faults are not easily detectable at the winding terminals by unbalance current or voltage.