Complete Selfprotection Technolgy to Minimize the Failures Of distribution transformer

7/28/2019 Complete Selfprotection Technolgy to Minimize the Failures Of distribution transformer.

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Sambit Sunyani

Regd no: 0901132


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The high rate of failure of secondarydistribution transformer in power systemsmay perhaps be described as one of thetragedies of distribution system managementof present times in India. The advent of CSPtechnology has encouraged progressivemanufactures to go in for high performancedistribution transforms. CSP technologyenables a transformer to protect itself fromfaults.


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Transformer is a static device used fortransferring power from one circuit toanother circuit without changing frequency.

In its simplest form, transformers consist oftwo conducting coils having a mutualinductance linked by a common magneticflux through a path of low reluctance.

The coil which receives power is calledprimary winding and the coil which deliverspower is called secondary winding.


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EMF equation of transformer E=4.44fN

Types:

single phase transformer

Three phase transformer


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Core Winding

Tank

Conservator Bushings

Breather

Radiators


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Load monitoring on LT side and assessmentof overloads.

Cleaning of bushing and body.

Tightness of HV, LV, LA and earth connection. Functioning of breather and reconditioning of

silica gel and oil seal.

Periodic testing of transformer oil dielectric

and acidity.


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OVERLOAD:Over load for a short duration for transformerin service are unavoidable. To regularlymonitor all the distribution transformeragainst over load is equally impracticable,unless automated. Every transformer will benormally designed to with standard for anover load of 10% against its rating withreduced service life.


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Single phasing by unbalanced load:Ideally the three phase transformer should beloaded equally in al three phases. But this isimpracticable as the utility caters to several

single phase and three phase customers fromthe same transformers. This unbalancedcauses circulating currents in three phasedelta star connected transformer in the HV

delta winding develops heat and results infaster deterioration of HV winding.


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Low oil levels:If transformer oil leakage occurs in a

transformer due to loose tank top coverbolts, are a worn out gasket, this can lead tofailure of transformer winding.

Faulty termination:Some times it is possible that heavy sparkoccur on LV terminal of the transformer dueto improper connections i.e., loose

connections, not using flat washer, springwasher, check nuts etc or connecting thecable with out bi metallic strips.


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Unclear LT line faults:Improper tree clearance can result in high

faults which are similar to over loads and cancauses failure of equipment.

Improper earthing Poor quality of LT cable Improper installation & maintenance Improper design and manufacture


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CSP technology shows the way out of thesedistressing situations discussed earlier.

CSP technology enables a transformer toprotect itself from faults.

The transformer is protected from persistent

over loads not cleared by conventionalprotective gear and causing dangeroustemperature rise.


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1. Primary side: a)Air break switch (external) b) Horn gap fuse (external)

c) Primary Fuse (internal)

2. Secondary side: a) circuit breaker (internal)

b) Secondary fuse (external) c) surge arrester


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Primary (high voltage fuse): Power utilities in India provide a HG fuse on

primary side of a distribution for systemprotection. It has the following demerits,

It is exposed to wind and rain and becomesmechanically week very soon and blowsfrequently.

It is vulnerable to tampering by eagerconsumers especially in Rural areas whowould replace a blown fuse, with availablefuse wire.


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Solution:

In a CSP transformer, the primary fuse which

fulfills the above requirements is placed in serieswith the primary winding.

This fuse is normally mounted inside of the

primary bushing and is connected via a terminalblock to the high voltage winding.

The purpose of this expulsion fuse is to protectthe part of the electrical distribution system,

which is a head of the transformer from faultswhich occurs inside of distribution transformer.


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Secondary (low voltage circuit breaker): For over load and secondary fault protection

signal light, the emergency control magnetictrip is used.

The low voltage circuit breaker is the centralcomponent of the CSP protection package. Itis this circuit breaker which provides theentire over current protection to the

transformer in order to perform this criticalfunction its thermal characteristics and thetime response to the thermal changes mustmatch those of the transformer.


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Secondary fuse: It is an external fuse, connected in series with

phase. It has low resistance with short pieceof aluminium wire. If any fault occurs on loadside secondary fuse will blown.

Surge arrester: The closer the surge arrester can be mounted

to the transformer, the shorter will be theground lead connection between the arrester

and the transformer. The shorter thisconnection. The less will be the lighting surgeinduced voltage stress on the transformerwinding.


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Thermal protection of transformer:

The average temperature of the transformerwinding at any time is given by the average oiltemperature plus the average windingtemperature rise due to the instantaneous loadcurrent

One of the functions of the circuit breaker is tomake sure that this pre determined value ofaverage winding temperature is not exceeded.

The CSP circuit breaker in order to be universallyapplicable to all transformers and thermalconstraints has protective characteristics whichare sensitive to the same thermal inputs as thetransformers.


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Secondary fault protection: The other importantfunctions of the CSP circuit breaker. The CSP circuit breaker will respond to secondary faults

external to the transformer by tripping open, and in mostcases, this action prevent any thermal damage occurring tothe transformer.

When the simple action of reclosing the CSP circuit breaker iscompared to the action required in the case of a non CSPtransformer where either a primary fuse or secondary fusemust be replaced, the benefits of CSP technology is apparent.


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CSP circuit breaker constructional features: It is an electromechanical device with three major

elements.

Temperature sensing( using bimetallic strip).

Latching and Tripping.(The latching tripping functions of the circuit breaker

are carried out with an assembly of parts quite similarto those used in industrial type air circuit breakers.Other features that are built in to the latching andtripping functions are)a)The signal light latch (gives visual indication).b)The emergency control assembly (restores supply by

closing circuit breaker in urgent need of power).c)The magnetic trip device. (increases opening speed).

Current interrupter


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Benefits of CSP technology Lower installed cost There is no need for separate mounting

arrangements for primary fuse, surgearrester, low voltage circuit breaker andconnecting leads.

Less installation time: A non CSP installation takes twice as long as

a CSP installation. Easier and simpler installation. less external connection and spacing for

electrical clearance.


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Automatic load management: The CSP signal light at each transformer

provides information about loadingconditions. This can be used by the powerdistribution company to manage the loadingon the transformer to insure the best

economic use of each size transformer. Lower cost of operation and maintenance. Near appearance: CSP transformer installation presents a much

cleaner and uncluttered appearance.


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CSP technology has paved the way to high

performance distribution transformer and betterdistribution system management

The faulty transformer is isolated and onlyconsumers served by transformer are affected

It enables a transformer to protect itself fromfaults. The transformer is too protected fromover loads not cleared by conventional protectivegear and causing dangerous temperature rise.

The distribution system to which it is connected

is protected from a transformer that has failed.The faulty transformer is isolated and onlyconsumers served by transformer are affected.


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Complete Selfprotection Technolgy to Minimize the Failures Of distribution transformer