978-1-5386-6159-8/18/$31.00 ©2018 IEEE

Measurement of Radio Interference Emission Around +/-100 MVAR STATCOM Valve Building

Near 400/220 kV Substation P. Rajamani K. Urukundu and Pradeep M Nirgude

Central Power Resarch Institute Ultra High Voltage Research Laboratory,

Hyderabad, India Email: rajamani@cpri.in, pmnirgude@cpri.in

Abstract— Flexible AC Transmission System (FACTS)

devices are inevitable to improve the performance of power supply system having the interconnection with solar and wind forms. The firing of converter valves of these large power electronics devices emits radio interferences, which may disturb the operation of nearby other delicate electronics devices. CIGRE, CISPR and IEEE had given guidelines for limits, analytical calculation, measurements and attenuation. In the present work the experiences of measuring radio interference around the valve hall is elaborated for three different operating conditions, including while injecting reactive power into the grid from STATCOM unit.

Keywords—Radio Interference, STATCOM, RIV measurement, Reactive power injection

I. INTRODUCTION

An increase in electric power demand and concerns on depletion of natural resources has led to generation of electric energy from renewable energy sources, particularly solar and wind farms. Due to less maintenance, economic and no wear and tear, the solar photovoltaic power generation had emerged as one of the important renewable energy generating system. Many utilities had installed Ultra-mega solar power projects for large power generation. However, one of the major issues in the solar power project is the integration solar farms to the grid, which may introduce power system performance issues. Among that the voltage stability is the major concern. The conventional series and shunt compensating devices connected in the grid maintain the voltage magnitude by injecting/absorbing reactive power which not only improves the maximum power transfer capability of power network but also improves power quality. To address the dynamic changes in the power system stability issues, the slow response of conventional devices need for adoption of advanced control techniques, viz. flexible AC transmission system (FACTS) to stabilize the grid power and voltage. Static synchronous compensator (STATCOM) is one of the important FACTS devices and commonly used to improve the power supply system performance.

STATCOM device essentially consists of inverter with metal oxide semiconductor field effect transistor (MOSFETs) or insulated gate bipolar transistors (IGBTs), capacitor, reactor and filters. Enhancement of power supply system performance requires frequent switching ON and OFF of FACTS devices. This continuous stream of turning ON- turning OFF power electronic devices, i.e., thyristor valves, generates steady state electromagnetic high frequency noises. Without any suppression measures this radio noise emitted from FACTS devices could be intolerable [1] and the propagation of this noise by conduction or radiation may

affect the performance of nearby delicate control and communication devices.

In recent years, to improve the performance of high voltage transmission lines the FACTS devices are widely used and the electromagnetic interference emission from that became inevitable. Therefore, it is necessary to measure and to apply suitable methods, viz. electromagnetic shielding by metallic screen and filters, to reduce noise level to an acceptable value, else the unwanted radio interference signal may cause malfunctioning of nearby electronic devices. Hence, it is mandatory to validate the electromagnetic interference emission from valve hall to provide uninterrupted, quality and reliable power to the consumer.

The paper presents experiences on measurement of radio interference voltage around the shielded converter valve building consisting of +/- 100 MVAR STATCOM unit near the 400 kV switchyard. The influence of VAR injection into the grid, attenuation due to lateral distance and effect of nearby energized objects on the radio interference voltage measurement is also elaborated.

II. MEASUREMENT SITE DETAILS

The radio interference voltage emission measurement performed at 400/220 kV PGCIL sub-station of N.P Kunta, Andhra Pradesh, India. The station is receiving power from the nearby Ultra Mega Solar Park. For reactive power compensation, the station is having two STATCOM units each of +/- 50 MVAR, in total, +/-100 MVAR STATCOM. Each +/- 50 MVAR STATCOM units is designed with the 18 level multi modular based voltage converters. The STATCOM valve hall is shielded with 1mm thickness iron mesh of 50x50 mm for radio interference emission attenuation. However, the reactive power is supplied / absorbed from the 400 kV double circuit line through the 33/400 kV coupling transformers installed in the each phase. The air compressors and water cooling systems are installed around the building for the heat dissipation of the STATCOM units. A 400 kV switchyard is located at a distance of 50 m (approximately) from the STATCOM valve hall and was energized during all the measurements.

III. METHOD AND EQUIPMENT USED FOR RADIO

INTERFERENCE (RI) MEASUREMENT

In general the electromagnetic interference (EMI) is

measured either by radiated or by conducted method. EMI of high voltage equipment is measured at 1 MHz frequency using EMI test receiver in conjunction with coupling capacitor at high voltage testing laboratories, is referred as conducted method. On the contrary, the frequency spectra of radio noise emitted from the transmission lines, substation

Proceedings of the National Power Systems Conference (NPSC) - 2018, December 14-16, NIT Tiruchirappalli, India

equipment and converter valve stations, etc., at wide range of frequencies of interest, ranging from 0.15 to 30 MHz are measured using suitable EMI test receiver along with appropriate antenna [2]. The radio noise emitted from such equipment higher than 300 MHz are so low and the interference is unlikely to be caused to television reception [3]. All the measurements are performed using Quasi-peak detector.

In the present work, the radio interference voltage spectra are measured at discrete frequencies range of 0.15 to 30MHz. The frequencies, band width, charging and discharging time and EMI test receiver used for measurement is given in Table 1. The measuring equipment is in compliance with CISPR 16-1-1 [3] (International Special Committee on Radio Interference) and method used for measured in general accordance with CISPR 18-2:2017 and IEEE 403:2017 [4]. The photograph of the EMI test receiver ESVS 10 is shown in Fig. 1.

TABLE 1: EMI TEST RECEIVER USED FOR RI MEASUREMENT

EMI test receiver Make & Model

Frequency

Range (MHz)

Antenna used

Band width

6 dBμV/m

(kHz)

Charging and Discharging time of quasi peak detector

(ms) M/s. R&S Germany ESHS 10 (9 kHz to 30 MHz)

0.15 to 30

Loop (Make:

M/s. R & S)

9 1 ms and 160 ms

M/s. R & S, Germany ESVS 10

(20 to 1000 MHz)

30 to 1000

Bi-conical (Make.:M/s. R & S,)

120 1 ms and 550 ms

Fig.1. EMI Test receiver ESVS 10 (Frequency Range 20 MHz to 1000 MHz)

According to the frequency of interest, two different antennas, viz. loop and bi-conical antennas are used to measure the radio noise level in the frequency range of interest, i.e, 0.15 to 30 MHz. The dimensions and other technical parameters of these antennas are in compliance with CISPR 16-2[3]. The photograph of loop and bi-conical antennas during the measurement is shown in Figs. 2 and 3, respectively. During the measurements, the loop antenna was placed at a height of 2 m from the ground with help of the tripods. The Bi-conical antenna is placed at a height of 3 m from the ground.

During the measurements position of the loop antenna is adjusted to a value from 0 to 180 degrees in such a way that

to read maximum radio interference at that position at 500 kHz frequency. At that orientation it is fixed in tripod at a height approximately 2 m to avoid human error. The orientation of bi-conical antenna to the measuring site is adjusted to get the maximum radio interference at particular frequency and fixed in that position during measurement. This procedure is repeated for during each measurement.

Fig.2. Loop Antenna fixed at a height of 2m for RIV measurement

Fig.3. Bi-conical Antenna for RIV measurement

Proceedings of the National Power Systems Conference (NPSC) - 2018, December 14-16, NIT Tiruchirappalli, India

The radio interference is measured for three different operational conditions, viz.

A. STATCOM is ON and the Gating controls of Thysistor valve are OFF

B. STATCOM is ON and the Gating controls of Thysistor valve are ON but no reactive power either observed or injected and

C. STATCOM is ON, Gating controls of Thysistor valve are ON and the reactive power injected into the 400 kV grid using 33/400 kV coupling transformer.

The measurements were carried at ten locations around the STATCOM value building. A 400 kV switchyard was near the STATCOM building at a distance of approximately 50 m and energized at all the time during measurement. As the switchyard is nearby, radio noise measured during the operation condition, STATCOM ON and controller OFF is considered as the background noise at that location.

IV. RESULTS AND DISCUSSIONS

A. Measurement of RI at lateral distances from valve hall

The frequency spectra of radio interference( RI) from the valve hall due to direct radiations is measured at two different places near the vicinity building at a lateral distance of 6 m and 26 m, respectively. At each location, measurements are carried out with two different operational conditions, a) STATCOM ON, Gating control to the Thyristor is OFF and b) STATCOM ON, Gating control to the Thyristor is also ON, in the frequency range of 0.15 to 30 MHz using the suitable EMI test receiver and antenna. The weather and other operation conditions for RI measurement at lateral distances of 6 m is given in Table 2.

TABLE 2: WEATHER AND OTHER OPERATING CONDITIONS OF A AND B

Sl. No.

Parameter Particulars / Status of operating Condition A Condition B

01 Distance of

measurement from valve hall building

6m

02 STATCOM Valve Gating Controller

OFF ON

03 MVAR injected into

the grid Zero

04 400/220 kV sub-

station Charged condition at a distance of 50 m

(approx.).

05 Method applied for reduction of noise

emission

Metallic wire mesh around the valve hall with 1 mm thickness and 50 ×50

mm size 06 Weather conditions Fair and dry with clear sky

07 Dry Bulb

temperature (Td ˚C) 32˚C

08 Wet bulb

temperature (Tw ˚C) 28˚C

The frequency spectra measured when the converter

gating control in OFF state is considered as background noise. The frequency spectra of RI at 6m distance with operational conditions A and B is shown in Fig.4.

To understand the effect of lateral attenuation, the

frequency spectra is measured at a lateral distance of 26 m with the operating and other conditions as stated in Table 2. The lateral attenuation of radiated interference of RI is shown in Fig.5. It is evident from Fig.5, though the installed

wire mesh reduced the radio noise emitted from valve hall due to radiation in the frequency of interest, the interference measured at 26 m is lower than that of 6 m due to lateral attenuation of radiated noise.

Fig.4. Frequency spectra of RI at 6 m distance from STATCOM valve building with gating controller is in OFF and ON state

Fig.5. Effect of lateral distance on the RI during STATCOM valve gating control ON state

B. Measurement of RI during reactive power injected into grid

To understand the impact of reactive power injection /

absorption into the grid on radio interference noise emitted from STATCOM unit, the frequency spectra of interference is measured at close vicinity of valve hall, i.e. at 6 m lateral distance. Measurements were performed on all three operating conditions of STATCOM as stated earlier. Weather and other operating conditions during three measurements are given in Table 3. Measured frequency spectra of Radio Interference are shown in Fig.6.

Radio noise emitted from the converter valve station mainly depends on amplitude of voltage collapse at the valve firing and time of this collapse. The magnitude of radio noise is not depends on whether reactive power is injected into grid or not. Further, at site, the reactive power injected to grid using 33/400 kV coupling transformer and it

Proceedings of the National Power Systems Conference (NPSC) - 2018, December 14-16, NIT Tiruchirappalli, India

may have some influence on radio noise emission. Since, it is evident from the Fig. 6, the reactive power injection to the grid is not having any considerable impact on the radio noise emitted other than a small contribution from coupling transformer and other accessories.

TABLE 3 WEATHER AND OTHER OPERATING CONDITIONS OF A, B AND C

Sl. No.

Parameter Particulars / Status

Condition A

Condition B

Condition C

01 Distance of

measurement from valve hall building

6 m (Opposite direction to the measurement locations shown in section

IV. A.)

02 STATCOM Valve Gating Controller

OFF ON ON

03 MVAR injected

into the grid Zero

+/- 100 MVAR injected

04 400/220 kV sub-

station Charged condition at a distance of 50 m

(approx.).

05 Method applied for reduction of noise

emission

Metallic wire mesh around the valve hall with 1 mm thickness and 50 ×50 mm size

06 Weather conditions Fair and dry with clear sky

07 Dry Bulb

temperature (Td ˚C) 35˚C

08 Wet bulb

temperature (Tw ˚C) 29˚C

Fig.6. Frequency spectra of RI with all three operational conditions at a distance of 6m from valve hall

C. Impact of nearby energized objects in RI measurement of valve hall

The radio interference noise is measured inside the 33

kV switch yard, used to interconnect the STATCOM unit and 400 kV grid, longitudinal distance of 14 m from the valve hall. This measuring point is in close vicinity of coupling transformer, bushing, bus bar and other accessories of 33 kV switch yard. The operating conditions and physical parameters during measurement is given in Table 4. The photograph of the measuring point is shown in Fig.7.

The frequency spectra of radio interference measured is

shown in Fig.8. It is evident from Fig.8 that, though the reactive power injection to the grid is not having any impact on the RI measured, but, the highest RI is measured in this location at 0.25 MHz frequency. However, the background

measured at this location, when the 33 kV switch yard is OFF, is comparable with the interference measured in other locations. Hence, the highest radio interference recorded may be due to the influence of interference from the nearby switch yard accessories when energized.

Fig.7. RI measurement using loop antenna inside the switch yard at a distance of 14 TABLE 4 WEATHER AND OTHER OPERATING CONDITIONS OF A, B AND C

Sl. No.

Parameter Particulars / Status

Condition A

Condition B

Condition C

01 Distance of

measurement from valve hall building

14 m, located inside 33 kV switch yard

02 STATCOM Valve Gating Controller

OFF ON ON

03 MVAR injected

into the grid Zero

+/- 100 MVAR injected

04 400/220 kV sub-

station Charged condition at a distance of

50 m (approx.).

05 Method applied for reduction of noise

emission

Metallic wire mesh around the valve hall with 1 mm thickness and 50 ×50 mm

size 06 Weather conditions Fair and dry with clear sky

07 Dry Bulb

temperature (Td ˚C) 36˚C

08 Wet bulb

temperature (Tw ˚C) 31˚C

Fig. 8. Impact of RI measured under the influence of nearby energized objects

Proceedings of the National Power Systems Conference (NPSC) - 2018, December 14-16, NIT Tiruchirappalli, India

V. CONCLUSIONS

The experiences of radio interference (noise) measurement around the +/- 100 MVAR STATCOM valve building near 400/220 kV substation under three different operating conditions using antennas and EMI test receivers are elaborated. It was observed that while the gate firing of the devices of the STATCOM does affect the RF noise, reactive power injection to the grid does not have any influence on the measured radio interference noise level. Further noise attenuation may be possible with improved design of nearby 33 kV and 220 kV switch yard.

ACKNOWLEDGMENT

The authors wish to thank both the management of Central Power Research Institute (CPRI) and POWERGRID Corporation of India (PGCIL) for extending permission to carry out this work. Thanks also due to Mr. G.Sureshkumar and employees of 400/220 kV PGCIL substation, NP Kunta for their assistance during the measurement.

REFERENCES [1] TR CISPR 18-2:2017, “Radio interference characteristics of overhead

power lines and high voltage equipment, Part 2: Methods for measurement and procedure for determining limits”

[2] CIGRE/CIRED C4.202: 2009, “Guide for measurement of radio frequency interference from hv and mv substations”

[3] TR CISPR 16 Specifications for radio disturbance and immunity measuring apparatus and methods

[4] IEEE Std. 430:2017, IEEE standard procedure for the measurement of radio noise from overhead power lines and substations.

Proceedings of the National Power Systems Conference (NPSC) - 2018, December 14-16, NIT Tiruchirappalli, India