Installation of Instrument Transformers at High Altitude - Ed1 2015-06-10 1HSM 9543 41-02en

8/16/2019 Installation of Instrument Transformers at High Altitude - Ed1 2015-06-10 1HSM 9543 41-02en

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Installation of instrument transformers at high altitudeEffects, problems and solutions

Tec hni cal inf orm ati on

To reduce the risk of insulation failureto an economically and operationallyacceptable level, it is important thatthe insulation withstand of substationequipment should be selected withregard to the expected over-voltagesoccurring during the normal operationof the substation. Important in thisaspect is of course the protectioncharacteristics of the installed surgearresters.

Since the air pressure is lower at highaltitudes, the dielectric strength ofcomponents will be lower. For thisreason, longer insulators may beneeded.

For high altitude installations the thermalbehavior and the withstand voltage forthe external insulation of the instrumenttransformers are affected by thereduction of air density.

Service conditions for instrument transformers are in IEC

61869-1 divided into two groups:

1. Normal service conditions. This group considers installation at an alti tude be low 1000m. Normal limit for temperature rise and standard insulationlevels as per IEC 61869-1 table 2 are applicable.

2. Special service conditions. This group considers installation at an alti tude above 1000 m,installation in areas with daily average temperature of morethan 35 °C and areas with seismic activity.

Current transformer IMB 145

The reduction of air density at high alt itude installat ions means

that the cooling ability of the air is reduced and temperaturerise limits of internal parts of the instrument transformer, forinstallation at an altitude above 1000 m, must be reduced.

The reduction factor for oi l immersed instrument transformersis 0.4% per 100 m above 1000 m


2/82 Technical information | ABB Instrument Transformers

Altitude correction for external insulation The reduced air density at high alti tude installat ions has aneffect on the disruptive voltage of the external insulation.For installations at an altitude higher than 1000 m, the arc-ing distance under the standardized reference atmosphericconditions shall be determined by multiplying the withstandvoltages required at the service location by a factor k in ac-cordance with Figure 2 of IEC 61869-1.

The dielectr ic s trength of the interna l insulation is no t affectedby the altitude.

The correction factor for external insulation is per IEC 61869-1according to the formula:

m = 1.0 for power frequency voltage and LIWL and 0.75 for SIWLH = altitude above sea level in meters.

From Figure 2 it can be concluded that an instrument trans-former intended for installation at an altitude of 3000 m shallhave an external flashover distance able to, at altitude


3/8 ABB Instrument Transformers | Technical information 3

ABB solutionIn order to illustrate this, on page 5 and 6 we show someexamples of how the high altitude installation are handled by

ABB. The examples cover current transformers of the typeIMB and capacitor voltage transformers of the type CPB forthe system voltages 145, 245 and 550 kV for installations ataltitudes up to 4000 m.

The internal h igh voltage insu lation of the inst rument trans-formers is not affected by the installation altitude. Highvoltage testing, at altitude



0 1000 2000 3000 40000.80

0.85

0.90

0.95

1.00

Altitude (m)

KorrectionK

0

Figure 1. Altitude correction factor for the temperature rise

The alti tude correct ion factor for the temperature rise is perIEC 61869-1 according to the formula:

− ∆ T h temperature rise at an altitude h >1000 m and− ∆ T h0 limits of temperature rise ∆ T at al titudes ≤ 1000 m

Example A current t ransformer shall be installed at an al titude of 3000m. The temperature rise type test performed in a laboratorylocated



System voltage 145 kV Current transformer IMB 145

1. Standard design IMB 145 up to altitude 1700 m

2. Standard design with flashover distance 1330 mm, foraltitude 1700 - 2800 m

3. Standard design with flashover distance 1600 mm, foraltitude 2800 - 4000 m.

System voltage 145 kV Capacitor voltage transformer CPB 145

1. Standard design CPB 145 up to altitude 1700 m



1000

Altitude (m)

1500 2000 2500 3000 3500 4000

250

275

300

325

350

400

425

450

375

Corrected test voltage 275 kV

Correctedtest voltage (kV)

1 2 3

1000

Altitude (m)

1500 2000 2500 3000 3500 4000

250

275

300

325

350

400

425

450

375



1 2 3

ABB standard designs for different altitudes

Current transformer IMB 145 Capacitor voltage transformer CPB 145



ABB standard designs for different altitudes


1. Standard design IMB 245 up to altitude 2000 m



1000

Altitude (m)

1500 2000 2500 3000 3500 4000

450

475

500

525

550

600

625

650

675

575



1 2 3

1000

Altitude (m)

1500 2000 2500 3000 3500 4000

450

475

500

525

550

600

625

650

675

575



1 2 3 4

Current transformer IMB 245 Capacitor voltage transformer CPB 245


1. Standard design CPB 245 up to altitude 2000 m



4. Standard design with flashoverdistance 2800 mm, for altitude3500 - 4000 m.




1. Standard design IMB 550 for altitude 3000 m.


1. Standard design CPB 550 for altitude


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Contact us

ABB ABHigh Voltage Products Instrument TransformersSE-771 80 Ludvika, SwedenPhone: +46 (0)240 78 20 00E-mail: [email protected] www.abb.com/highvoltage

©Copyright 2015 ABB All rights reserved

NOTE! ABB AB is working continuously to improve the products.

We therefore reserve the right to change designs, dimensions and data

without prior notice.

Installation of Instrument Transformers at High Altitude - Ed1 2015-06-10 1HSM 9543 41-02en

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