Process level development strategies

The MAIN JOURNAL for POWER GRID SPECIALISTS in RUSSIA

2014

DIGEST, February, 2014

32

Digital substations

Digital sensor high-voltage test (35 kV).

A 

few years ago the terms “smart grid” or “digi-
tal substation” could be used only by young 
enthusiastic specialists as something very far.

But interest in smart grid inevitably 

grew, pro-active research, testing and development were 
carried out, and today the Government has made several 
strategic documents determining energy development in 
Russia. “Policy objective will be creation of intelligent 
electric grid complex with active-adaptive power system 
— new generation customer-oriented network based on 
the multi-agent control principle on the basis of mass 
balanced implementation of modern technological tools 
and solutions in the complex”, as set out in “Development 
Strategy of the of electric grid complex.” Thus, all 
the approved government documents directly refer us 
to creation of "Smart grids" in Russia, where digital 
substation are the key part.

In correspondence with IEC 61850 «Communication 

Networks and Systems in Substations» a digital substation 
has three levels:
•  

process 

level;

•  

bay 

level;

•  

station 

level.

The station and bay levels are the most widely covered 

and elaborated by Russian and foreign enterprises. 
These levels are responsible for control, monitoring, 
storing and distribution of data. Process level is not 
paid so much attention to, although it is responsible for 
collection of primary analog and discrete data, that is, 

Process level development strategies

Dmitry UKRAINSKIY (Дмитрий УКРАИНСКИЙ),  Leading Engineer,

Alexander ZHUKOV (Александр ЖУКОВ), Director General,

 TERMA-ENERGO LLC leading engineer

primary information. This includes current and voltage, 
presence or absence of voltage, busbars and transformer 
temperature, cables insulation resistance and other 
signals. Some of the most important decisions are made 
basing on this information, so it must not be forgotten 
that modernization and development of sensors collecting 
primary information in substations is very important.

Our company has secured its place in the market 

and established itself as a manufacturer and supplier of 
quality components for power industry, such as voltage 
detectors, voltage arc protection devices equipped with 
f iber-optical sensors, voltage dividers, and others. 
Also, our company develops and manufactures various 
products for 6—35 kV electrical equipment using epoxy 
compounds (post and entrance insulators, busbars). To do 
this TERMA-ENERGO LLC uses latest 3D technology 
for insulator and injection moulds design as well as 
modern equipment and technological processes acquired 
from the world leaders in this field, such as Hübers, 
Vogel, Hedrich, Huntsman. This combination allows 
TERMA-ENERGO to maintain high product consumer-
grade.

Development of modern element base and the adop-

tion of new international standards provided a good op-
portunity for our developers to use innovative approaches 
to gathering primary information necessary to create ad-
vanced digital substations. Based on the existing problems 
in the world experience in running the digital stations, a 
clear understanding and concept to establish a harmonized 
set of devices for collecting primary information has been 
generated. Today it is one of the priority directions of 
TERMA-ENERGO activity. This primarily concerns ac-
quisition of current and voltage data for commercial ac-
counting and protection. 

Contrary to popular belief about the preferential use of 

digital optical transformer at the substation process level 
we should not forget that such transformers are most ap-
propriate and effective at high and extra high voltages. 
While at medium and low voltages due to their high cost 
and low sensitivity these transformers are not effective.

On the base of lengthy research our company has been 

successful in developing high accuracy current and voltage 
sensors outputting digital optical signals of currents and 
voltages measured in real time. Workable specimens were 
obtained and test results proved their effectiveness.

Current sensor consists of a specially designed high-

precision, high-speed and jam-protected analog-to-

www.eepr.ru

33

digital conversion board and original 
measuring elements. All of this is placed 
on high potential side, does not require 
insulation and additional power source. 
Thus, only an extra strong dielectric 
fiber optic cable with two optical fibers 
providing galvanic isolation is routed 
to low potential side.

The first fiber transmits billing cur-

rent values of 0.2s accuracy [1] / 256 
samples/cycle; the second fiber trans-
mits 10p accuracy [1] current data /80 
(90) samples/cycle for relay protection 
units.

The current output signal ratio for 

relay protection device is 8000% of rated primary current. 
Operating temperature range is -40° to +85° C. The rated 
primary current is up to 5000 A.

Overall dimensions and weight of the current sensor is 

relatively small and can be commensurate with the classic 
measuring current transformer for 0.66 kV voltage. There-
fore, mechanical strengthening of high-voltage bus to in-
stall the sensor is not required. Dimensions and weight al-
most do not change under the increase of the rated current 
within 10—110 kV voltage class. As for the cost of the 
current sensor, it is a sequence lower in comparison with 
cost of transformer based on optical laws and commensu-
rate with cost of classical measuring current transformers 
starting from 10 kV voltage class.

Currently voltage sensor has an accuracy of 1%, and 

operates within -25 º — +50 º C temperature range. This 
sensor features a smaller dimensions and lower cost com-
pared to existing measuring voltage transformers, it has 
no DC magnetizing and resonance phenomena inherent to 
classical voltage transformers. Work is underway to in-
crease the accuracy of the sensor to class 0.2 [2] for use in 
commercial accounting of electric circuits. Digital output 
is similar to the output of current sensor.

To work on IEC 61850 standard these current and 

vol-tage sensors require digital Merging Unit, capable of 
receiving input digital optical signals and form a group 
digital stream protocol per IEC 61859-9-2LE standard. 
Using only digital signals, the accuracy of the informa-
tion received is maintained as digital optical signal car-
rying information from the transformer is not affected by 
electromagnetic interference and, in addition, there is no 
analog-to-digital conversion, which inevitably introduces 
additional error. Moreover, lack of an analog-to-digital 
conversion greatly simplifies Merging Unit and reduces 
the dimensions.

In accordance with policy we seek to identify and work 

through the most weaknesses and continuously engaged 
in the development of sensors to collect other valuable in-
formation except for current and voltage. The next device 
to be launched into serial production will be a tool for on-
line measurement of insulation resistance of cable lines. 
Due to constant connection of the device to high voltage, 

the time available for the measurement of this parameter 
takes about 5 minutes as opposed to the currently existing 
devices that perform the same task. The output signal may 
support GOOSE-messages.

Feasibility studies undertaken suggest that the cost of 

our equipment during the transition to serial production 
will not exceed the cost of conventional solutions and will 
provide a number of technical advantages:
•   

improving measurement accuracy and information 
transfer reliability;

•   simplicity of design, operation and maintenance;
•   unified platform data exchange (IEC 61850);
•   high noise immunity;
•   high fire explosion and ecological compatibility;
•   digital signal in real time;
•   absence of saturation and ferroresonance;
•   small size and weight of the primary equipment;
•   reduction in the number of copper cable connections, 

number of devices, as well as more compact arrange-
ment.
So, due to the advent of IEC 61850 standard unified 

data exchange platform made a reality transfer of 
information using innovative devices, including digital 
current and voltage transformers. However, a number 
of questions remains to be solved and full integration of 
these technologies providing smooth operation needs a 
joint effort of manufacturers and developers operating in 
the field of digital substations. Our company is open for 
cooperation.

LITERATURE:

1. GOST 7746-2001 “Current transformers. General 

specifications”

2. GOST 1983-2001 “Voltage transformers. General 

specifications”.

Ltd, Bldg 3, Dudko str., Saint-Petersburg, 192029

Tel. +7 812-640-11-28, +7 812-346-50-09

http://terma-energo.ru

ukrainskiy@terma-spb.ru