Voltage and Turn Ratio Test of Transformer

Voltage and Turn Ratio Test of Transformer 

Page 1

El ec t ri ri c al al Po w er er Sy st st em em Eng i neer in ing

HOME

BASIC ELECTRICAL

Sund ay , 05t h Aug us us t, t, 2012

TRAN TR ANSF SFO ORM RME ER

SWIT SW ITCH CHGE GEAR AR

PRO PR OTE TECT CTIO ION N

Thi s s itit e i s v is is i t ed ed : 149583

FRE REE E CLA LAS SSIFIED

FORU RUM M

TRA TR ANS NSMI MIS SSI SIO ON

DIST DI STRI RIBU BUTI TIO ON

Transformer Ratio Test The performance of a transformer largely depends upon perfection of specific turns or voltage ratio of transformer. So   transformer ration test  is an essential type test of transformer. The voltage voltage shoul should d be applied only only in the high voltage voltage windin winding g in order to avoid avoid unsafe unsafe voltage. voltage. Electrical Power Transformer  Working Principl Principle e of Transformer  Transformer  Ideal Transformer  Theory of Transformer  EMF Equation of Transformer  Leakage Reactance of Transformer  Equivalent Equival ent Circui Circuitt of Transformer  Voltage Regulation Regulation of Transformer  Losses in Transformer  Open & Short Circui Circuitt Test Test on Tran Transforme sformer  r   Auto Transformer  Tertiary Winding of Transformer  Parallel operation of Transformers Transformer Cooling System Core of Transformer  Transformer  Transformer Insulating Oil Dissolved Gas Analysis of Transformer Oil Over Fluxing in Transformer  Three phase transformer  Current Transformer  Voltage Transformer  Instrument Security Factor  •  Accuracy Limit & Instrument Knee Point Voltage of Current Transformer  • Earthing Earthin g or Grounding Transformer  External & Internal Faults in Transformer  Backup Protection Protection of Transformer  Transformer  Differential Protection of Transformer  Restricted Earth Fault Protection Buchholzz Relay in Transformer  Buchhol Transformer Testing Transformerr windin winding g resistance measure measurement ment • Transforme Transformer Transforme r Ratio Test • Transformer  • Vector Group Test of Transformer  • Dielectric Test of Transformer  • Temperature Rise Test of Transformer  Transformerr Impulse Test • Transforme

Ratio test of transformer and check of phase displacement displacement  Actually the no load voltage voltage ratio of transformer is is equ equal to the the turn turn rati ratio o. So   r at at io io t es es t o f   transformer  Procedure Proce dure of transformer ration test

1) First, the tap changer of transformer is kept in the lowest position and LV terminals are kept open. 2) Then Then apply apply 3-phas 3-phase e 415 V suppl supplyy on HV terminals. terminals. Measure Measure the voltages applied applied on each phas phase e (P (Pha hase se--Phas Phase) e) on HV and and indu induce ced d voltages at LV terminals terminals simultan simultaneousl eously. y. 3) After measuring the voltages at HV and LV terminals, terminals, the tap changer of transformer should should be raised raised by one positi position on and repeat repeat test. test. 4) Repeat the same for each of the tap position separately. The above   transformer ratio test  can also be performed by portable Transformer Turns Ratio (TTR) Meter. They have an in built power supply, with the the voltages commonly used being very very low, such as 8-10 V and 50 Hz. The HV and LV windi winding ngss of one one phase phase of a trans transfor former mer are connected connected to the instr instrumen ument, t, and the intern internal al bridge bridge elemen elements ts are varie varied d to produ produce ce a null null indicat indication ion on the detector. detector. Let's Let's have have a discuss discussion ion on Transformer Transformer Turns Turns Ratio (TTR) Meter method of   turn ratio test of  transformer 

 A phase voltage is applied to the one of the windings by means of a bridge circuit and the ratio ratio of indu induced ced voltag voltage e is measur measured ed at the the bri bridge. dge. The accu accurracy acy of the meas measu uring instrument instrument is < 0.1 0.1 %

Search within ele electrical4u.com ctrical4u.com Search

-: PLEASE SUGGEST :-: TO IMPROVE THIS SITE :-: Your Full Name :-: Your Email Address :-: Your Phone Number :-: Your Place :-: Title of Your Suggestion :-: Your Suggestion :-

-: Security Code :-

Send

Delete

OBJECTIVE QUESTIONS QUESTIONS - TRANSFORMER 1 OBJECTIVE QUESTIONS QUESTIONS - TRANSFORMER 2 OBJECTIVE QUESTIONS QUESTIONS - TRANSFORMER 3 OBJECTIVE QUESTIONS QUESTIONS - TRANSFORMER 4 OBJECTIVE QUESTIONS QUESTIONS - TRANSFORMER 5 OBJECTIVE QUESTIONS QUESTIONS - TRANSFORMER 6 OBJECTIVE QUESTIONS QUESTIONS - TRANSFORMER 7 OBJECTIVE QUESTIONS QUESTIONS - TRANSFORMER 8

Voltage and Turn Ratio Test of Transformer 

Theoretical turn ratio =

HV winding voltage LV winding voltage

This theoretical turn ratio is adjusted on the transformer turn ratio tested or TTR by the adjustable transformer as shown in the figure above and it should be changed until a balance occurs in the percentage error indicator. The reading on this indicator implies the deviaton of measured turn ratio from expected turn ratio in percentage.  Measured turn ratio - expected turn ratio Deviation in percentage = X 100 % Expected turn ratio Out-of-tolerance,  ratio test of transformer  can be due to shorted turns, especially if there is an associated high excitation current. Open turns in HV winding will indicate very low exciting current and no output voltage since open turns in HV winding causes no excitation current in the winding means no flux hence no induced voltage. But open turn in LV winding causes, low fluctuating LV voltage but normal excitation current in HV winding. Hence open turns in LV winding will be indicated by normal levels of exciting current, but very low levels of unstable output voltage. The turn ratio test of transformer  also detects high resistance connections in the lead circuitry or  high contact resistance in tap changers by higher excitation current and a difficulty in balancing the bridge. Discuss on Electrical Transformer  - online forum List of  Transformer Manufacturers  in India

HOME | BASIC ELECTRICAL | TRANSFORMER | SWITCHGEAR | PROTECTION | TRANSMISSION Copyright 2012-13 © Electrical4u.com - Online Electrical Power System Engineering Study Guide

Page 2