Instrument Transformer (ALIV - BANGLADESH)
Post on 10-Nov-2014
668 Views
Preview:
DESCRIPTION
Transcript
April 8, 2023 1
Instrument Transformers
April 8, 2023 2
Good For Everything
Group
April 8, 2023
Group Members
3
Sl No.
NAME ID TOPIC
01 Mehedi Hasan
11105140
Introduction of Instrument X former
02 Abu Jauad Khan Aliv (Leader)
11105137 Design & Function of CT
03 Farzana Farzin Rimi 11105192 Types & Accuracy Limit of CT
04 Ab-E-Zamzam
11105199
Equivalent Circuit, Safety & Usage of CT
05 Prodip Kumar Das 11105136 PT Design & Function
06 Humayun Kabir
11105167
Error & cause of Error Of PT & conclusion
April 8, 2023
Overview1. Introduction to Instrument Transformer 2. Its Classification3. Design & Function of CT4. Construction, Accuracy Limit & Equivalent CKT5. Safety Precaution & Usage of CT6. Design & Function of PT7. Construction & Error of PT8. Cause of Error in PT9. Conclusion
4
Introduction
Isolating the protection, control & measurement equipment from the high voltages of a power systemSupplying the equipment with the appropriate values of current and voltage
Instrument transformers are necessary for
April 8, 2023 5
April 8, 2023
Types of Instrument Transformers
Two Types of Instrument X-formers
Current Transformer (CT) Potential Transformer (PT)
Current transformer & Potential transformer
6
April 8, 2023
Current Transformer (CT)
7
April 8, 2023
Like any other transformer, a current transformer has a primary winding, a magnetic core and a secondary winding
The primary winding of a current transformer is connected in series with the power circuit
The impedance is negligible compared with that of the power circuit
Design
8
April 8, 2023
The alternating current flowing in the primary produces a magnetic field in the core & induces a current in the secondary winding
The CT's primary circuit consists of a single 'turn' of conductor, with a secondary of many tens or hundreds of turns
The primary winding may be a permanent part of the current transformer, with a heavy copper bar to carry current through the magnetic core
Design
9
April 8, 2023
Function Reduce power system current
to lower value for measurement
Insulate secondary circuits from the primary
Permit the use of standard current ratings for secondary equipment
10
April 8, 2023
Current Transformer Construction
BAR PRIMARY WOUND PRIMARY
Primary
Secondary
11
April 8, 2023
Bar-Primary Type CT
RELAY
1A 1000A
1000 turns sec
Insulation covered wire, giving inter-turn insulation & secondary to core insulation
Generator, or system voltage source
‘Feeder’ or ‘Bus-bar’ forming 1 turn of primary circuit
Insulation to stop flash-over from HV primary to core & secondary circuit
Laminated ‘strip’ wound steel toroidal core
12
April 8, 2023
Accuracy
The accuracy of a CT is directly related to a number of factors
Burden Rating factor Load External electromagnetic fields Temperature Physical configuration. The selected tap, for multi-ratio CTs
13
April 8, 2023
Accuracy
• Burden The secondary load of a current transformer is
usually called the "burden" to distinguish it from the load of the circuit whose current is being measured
• Rating factor Rating factor is a factor by which the nominal
full load current of a CT can be multiplied to determine its absolute maximum measurable primary current 14
April 8, 2023
C.T. Equivalent Circuit
ZbN
P1
ZCT
S1
VtZe
IsIp
Ip/NIe
Es
Ip = Primary rating of C.T. Ie = Secondary excitation currentN = C.T. ratio Is = Secondary current
Zb = Burden of relays in ohms Es = Secondary excitation voltage
(r+jx) Vt = Secondary terminal voltage
ZCT = C.T. secondary winding across the C.T. terminals
impedance in ohms (r+jx)Ze = Secondary excitation
impedance in ohms (r+jx)
15
April 8, 2023
Safety Precaution
The secondary of a current transformer is not disconnected from its load while current is flowing in the primary
The transformer secondary will attempt to continue driving current across the effectively infinite impedance.
This will produce a high voltage across the open secondary
This high peaks of voltage may not be measured by conventional voltmeter. But these high peaks of induced voltage may breakdown the CT insulation, and may case accident to personnel
16
April 8, 2023
Usage
Current transformers
are used:
Measuring current
A CT for operation on a 110 kV grid
Monitoring the operation of the power grid
17
April 8, 2023
Potential Transformer (PT)
18
April 8, 2023
Design A Potential Transformer theory is just like
theory of general purpose step down transformer
Primary of this transformer is connected across the phases or and ground depending upon the requirement
PT has lowers turns winding at its secondary
In an ideal Potential Transformer when rated burden connected across the secondary the ratio of primary and secondary voltages of transformer is equal to the turns ratio
But in actual transformer there must be an error in the voltage ratio as well as in the phase angle between primary and secondary voltages
19
April 8, 2023
Types of Potential Transformer
Two main basic types are available:
Electromechanical VT`s Similar to a power transformer May not be economical above 132kV
Capacitor VT`s (CVT) Used at high voltages Main difference is that CVT has a capacitor
divider on the front end20
April 8, 2023
Construction of PT
a. Output – Seldom more than 200-300VA. Cooling is rarely a problem
b. Insulation – Designed for the system impulse voltage level. Insulation volume is often larger than the winding volume
c. Mechanical Design – Not usually necessary to withstand short-circuit currents. Must be small to fit the space available within switchgear
The construction of a voltage transformer takes into account the following factors
21
April 8, 2023
Provides isolation from high voltages
Must operate in the linear region to prevent accuracy problems - Do not over specify VT
Must be capable of driving the burden, specified by relay manufacturer
Protection class VT will suffice
Function
22
April 8, 2023
Errors in PT
Is - Secondary CurrentEs - Secondary induced emfVs - Secondary terminal voltageIp - Primary currentEp - Primary induced emfVp - Primary terminal voltageKT - numbers of primary turns/number of secondary turnsIo - Excitation Currentβ - phase angle error
The difference between the ideal value Vp/KT and actual value Vs is the voltage error or ratio error in a potential transformer
% voltage error = Vp − KT.Vs /Vp X 100 %
The angle β between the ′ ′primary system voltage Vp and the reversed secondary voltage vectors KT.Vs is the phase error
23
April 8, 2023
The voltage applied to the primary of the potential transformer first drops due to internal impedance of primary
Transformed voltage across secondary winding will again drops due to internal impedance of secondary before appearing across burden terminals
Cause of Error in PT
24
April 8, 2023 25
ConclusionCurrent Transformer
Measuring current
Monitoring the operation of the power grid
• CT secondary should not be kept open
Potential Transformer
Measuring Voltage Provides isolation from high voltages
April 8, 2023 26
THANK YOU
top related