How to prepare the specification of a 80/100MVA ONAN/ONAF transformer

Tap changing gear
i) Type
ii) Provided on
iii) Tap range
iv) Step Voltage
v) Rated voltage of on load tap changer
vi) Rated current of on load Tap changer
Over voltage operating capability and duration

Max flux density in any part of core and yoke at rated MVA ,normal voltage(Tesla)
Current density of HV /LV Windings
Insulation Levels for windings
a) 1.2 /50 micro – second wave shape impulse withstand (kVp)
b) Separate source withstand voltage (kV rms)
c) Power frequency voltage withstand (kVp)
Type of winding insulation
a) HV
b) LV winding
System short circuit level and duration for which the transformer shall be capable to withstand thermal and dynamic stresses (kA rms /Sec)
Noise level at rated voltage and frequency
Permissible temperature rise over ambient temp of 50 DC
i) Of top oil measured by thermometer
ii) Of winding measured by resistance
Minimum clearance in air (mm)
HV
a) Phase to Phase
b) Phase to ground
LV
c) Phase to Phase
d) Phase to ground
Terminals :
a) HV winding Line end
b) HV winding Neutral end
c) LV Winding
Bushing current rating
HV
LV
Max Radio Interference voltage level at 1 MHZ & 1.1 times max rms phase to ground voltage for HV Terminal Connector
Cooling Equipments
a) Number of Banks
b) No of Pumps
c) No of fans
Insulation level of bushings
a) Lightning impulse withstand (kVP)
b) Switching impulse withstand (kVP)
c) 1 Minute power frequency withstand voltage (kV rms)
d) Creepage distance (mm)
Bushing current transformers for purchasers use

(for restricted E/F protection)
i) Type
ii) Quantity
i) No of Cores
iii) Current Ratio (A/A): (A/A)
ii) Turn ratio
iv) Knee Point Voltage
v) Accuracy class
iii) Location for mounting
HV Neutral side CT for owners use
iv) Type
v) Quantity
vi) No of Cores
vii) Current Ratios (A/A)
viii) Turn ratio
ix) Knee point voltage
x) Class of accuracy
xi) Location for mounting
Bushing CT on LV side for load measurement
i) Type
ii) Current ratio
iii) Burden in VA
iv) Accuracy class
v) No of cores
LOSSES
Maximum acceptable (without any positive tolerance) no load loss (Iron Loss )at rated voltage and at rated frequency at 75 deg C in KW
Maximum acceptable (without any positive tolerance) load loss including cooler loss because of power consumption by the cooler fans ,motor pump sets etc at rated current and at rated frequency at 75 deg C in KW
Maximum acceptable (without any positive tolerance) Auxiliary Loss in KW
Connectors


How to achieve all those.Pls guide me in the calculation part
asked 9/24/2011
chandanasushma1
chandanasushma

1 Answer

Each of these is a reasonably involved calculation (or bit of research). Many of the parameters (fault ratings for example) will be a result of computer modelling of the system. Impulse and insulation levels are from standards and depend on the insulation coordination you are trying to achieve. CT parameters are calculated dependant on the system, relays and other devices. The IEC and BS transformer standards give guidance on specifying transformers (and for an 80/100 MVA transformer I think it is worth having a good understanding of these).

I think at this stage (for the project) someone should be using software to model the system, understanding the relevant standards, understanding the operating requirements of the transformer (and associated switchgear, tap-change control, etc). This all goes together to form the requirements of the specification. If you company is regularly involved in power system design, the would like also have existing specifications which could be modified for your case.
answered 9/26/2011 Steven McFadyen 246
Steven McFadyen

Your Answer

In order to provide an answer to this question, you must Login

I am flagging this question because...




10 inform moderator flags remaining

I am deleting this question because...




I am flagging this answer because...




10 inform moderator flags remaining

Flagging a Post

You have already flagged this post. Clicking "Remove Flag" below will remove your flag, thus reducing the count by one as well.

I am deleting this answer because...





Lightning Protection and Earth Electrode Resistance

Most installations involve some form of lightning protection system which is connected to an earth electrode.  The function of the earth electrode is to...

Low Voltage Circuit Breakers

Circuit breakers are switching devices whose primary function is to isolate parts of an electrical distribution system in the even of abnormal conditions...

Questions - Reputation and Privilege

Our question and answer system while letting you do exactly what it says, is much more.  It is a dynamic user driven system, where our users not only ask...

Load Flow Study – how they work

A load flow study is the analysis of an electrical network carried out by an electrical engineer. The purpose is to understand how power flows around...

Photovoltaic (PV) Panel - Performance Modelling

In an earlier note on the site [Photovoltaic (PV) - Electrical Calculations], the theory of solar (PV) cell calculations was introduced.  In particular...

Fault Calculations - Introduction

Fault calculations are one of the most common types of calculation carried out during the design and analysis of electrical systems. These calculations...

Periodic Electrical Installation Inspection – How Often?

How often installations are inspected is up to the owner of the installation, provided such durations do not exceed any regulatory maximums in force. ...

Switchboard - Forms of Internal Separation

IEC 61439 'Low-voltage switchgear and controlgear assemblies', specifies standard arrangements of switchboard (call forms of internal separation). The...

Understanding Motor Duty Rating

One of the comments on my Motor Starting Series was asking for something on duty cycles. Here it is. As a purchaser of a motor, you have responsibility...

Maxwell's Equations - Introduction

Maxwell's Equations are a set of fundamental relationships, which govern how electric and magnetic fields interact. The equations explain how these fields...

Our website uses cookies so that we can provide a better experience.
To learn more about what cookies are and how to manage them visit AboutCookies.org