2013 IEEE 1st International Conference on Condition Assessment Techniques in Electrical Systems

978-1-4799-0083-1/13/$31.00 ©2013 IEEE C A T C O N 2 0 1 3

Performance of High Voltage Protection cards used in Digital Telephone Exchanges

Subba Reddy B, Alok R Verma Department of Electrical Engg.

Indian Institute of Science Bangalore-560012, INDIA reddy@hve.iisc.ernet.in,

alokverma129@gmail.com

Sanjeevan Palit Dept of Electrical Engg

SASTRA University Tanjavur, INDIA

sanjee1_palit@yahoo.com

Anwesha Panda Dept. of Electrical Engg

National Institute of Tech Rourkela, Orissa, INDIA

anweshap444@gmail.com

Abstract— Surge voltages and currents in low ac power

circuits essentially occur due to natural lightning and switching phenomena. The other source of surge occurrence is probably due to the interaction of power systems and communication system. The damages caused due to these phenomena to telecom equipment or modules create undesirable loss of service to the society. This paper presents the simulation and experimental investigations carried out on two types of high voltage high current protection cards used in digital telephone exchanges. Special efforts were made to fabricate the surge generators as per the prescribed standards. The experimental results on the performance of two types of high voltage protection (HVP) cards for combination wave (1.2/50μs open circuit voltage and 8/20μs short circuit current) and ring wave surge voltages (100kHz 0.5µs) are studied, analyzed and presented.

Keywords— lightning surges, telecommunication, high voltage protection, ring wave, combination wave, surge generators.

I. INTRODUCTION

A. Generation of high voltage high current surges Natural lightning produces over voltages and surge

currents which affect the low-voltage power and telecommunication systems [1-3]. Switching activity in power systems result in fault initiation, interruptions etc. The magnitude of switching surges depends on the parameters like type of circuit, kind of breakers or switching devices used. These surges are transient over-voltages of short duration, with high amplitude and are superimposed on the sinusoidal voltage wave having duration of few microseconds and amplitude of several kilo-volts[6,8]. The surges may contain energy to cause partial, permanent damage or gradual degradation of electronic components leading to premature failure [9]. It has been proven in practice that power surges are the most frequent source of failure to the telecommunication electronic equipment compared to any other type of power abnormality. The severity and the consequence of such fault depend on the location of the damaged equipment inside the telecom network.

The basic requirements of the subscriber line protection in telecommunication switching systems is to provide personnel safety and to reduce the probability of exchange equipment damage due to over voltage and over currents caused by various abnormality [10].

The need for protection should be based on a risk assessment considering the cost and importance of the system,

electromagnetic environment at the particular site and probability of the damages. The protection levels and the type of protective methods should also be chosen based on the cost of installation and maintenance of protective devices [11].

B. High Voltage High Current Protection The basic block diagram of the high voltage high current

protection card (HVHCP) is shown in the Fig 1. The circuit basically consists of the (a) primary protection, (b) secondary protection, (c) the co-ordination element and the (d) ground protection.

Fig. 1. Block diagram for high voltage high current protection for digital telephone exchange.

Primary protection: Primary protection is provided to protect the equipment at the interface where the surge is encountered first. This protection is designed to divert or conduct the surge energy. Primary protection is slow operating, high current device and generally gas discharge (GD) tube is used for primary protection. Secondary protection: Primary protection operates above certain voltage up to which the protection is provided by secondary protection. Secondary protection provides the protection from power induction, earth potential rise and power contact. This protection is precise and fast acting low current generally provided by semiconductor devices.

Co-ordination element: The co-ordination element is provided to separate the operation of primary and secondary protection. Positive temperature coefficient thermistors (PTC) are used as the co-ordination element. PTCs are the current

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limiting devices and used within the range of self-restoring capability. PTCs are mainly intended to limit over currents of relatively long duration and normally PTCs won’t respond for switching transients or surges caused by lightning discharges. Protection ground: protection ground is the common ground formed by the ring terminal taken out of the card and which is shorted with both primary and secondary ground. When these over voltage strike the communication line it travels on the line and reaches the telephone exchanges. If the exchanges are left unprotected they may get destroyed as a result the telecom service may get disturbed which is totally undesirable. These elements are designed to protect the electrical devices from voltage spikes. The surge protection card attempts to limit the over voltage supplied to an electric device by either blocking or by shorting to ground any unwanted voltages above a safe threshold.

II. SIMULATION STUDY In the present work circuits shown in Fig.2 and Fig.3 are used for the generation of two recommended standard waveforms: 0.5µs-100kHz ring wave and 1.2/50µs and 8/20µs combination wave as per [1-3].

Fig. 2. Circuit for simulation of 100 KHz ring wave as per [1, 2].

Initially parametric simulation study was conducted for combination/hybrid wave of 1.2/50µs (open circuit voltage) and an 8/20μs current wave (terminal short circuit current) using simulink and 0.5μs-100kHz ring wave using Orcad pspice. Fig. 4 and Fig.5 show the circuit employed for simulation of combination waveform using simulink. The values of resistance, inductance, and capacitance are used from the circuit shown in Fig.3. A brief description of blocks shown in Fig.4 and Fig.5 are: powergui: is a graphic user interface which stores the equivalent simulink circuit in terms of state-space equation of the model, here continuous method was used. The step block generates step between two definable voltage levels and the ideal switch is used to switch on and off when triggered, the scope displays variation of signal input to the simulation time. The instantaneous current through any branch of circuit is measured using current measurement and instantaneous voltage between two nodes is measured using voltage measurement. The clock presents simulation time at each simulation step. The workspace block sends a signal and writes signal data to the matlab.

Fig. 3. Circuit for simulation Hybrid/Combination wave as per [1, 2].

Fig. 4. Simulink Circuit for simulation of 8/20µS waveform.

Fig. 5. Simulink Circuit for simulation of 1.2/50µS waveform.

Fig. 6, Fig. 8 and Fig. 10 show the nominal waveforms prescribed as per standard [3], while Fig. 7, Fig.9 and Fig.11 present the simulated waveforms using the circuits shown in Fig.2 and Fig.3.

III. EXPERIMENTATION

A. Experimental arrangement Telecom standards [1-5] recommend that both voltage and

current waveforms are to be subjected to the test samples at a time. Due to the non availability of the commercial generators in the market, efforts were made to fabricate the hybrid/combination wave and ring wave surge generator as per [1-5] by employing circuits shown in Fig. 2 and Fig. 3. The hybrid/combination wave and the ring wave are generated using special impulse capacitors which are charged through half-wave rectifier circuit fed through a high voltage transformer. The input voltage to the high voltage transformer is controlled by an autotransformer.

A series resistance is inserted between the rectifier and the impulse circuit to obtain isolation and to minimize the peaking

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Fig. 6. Nominal waveform for 1.2/50µS wave as per [3].

Fig. 7. Simulated waveform for 1.2/50µS wave.

Fig. 8. Nominal waveform for 8/20µS wave as per [3].

Fig. 9. Simulated waveform for 8/20µS wave.

of charging current. The specially designed switch will connect the charged capacitor to the wave shaping circuit involving air cored inductors. It may be noted here that the inherent losses present in the capacitors and inductors are not explicitly shown in the circuit. An additional wave shaping resistor is placed at the output terminal which would be

Fig. 10. Nominal waveform of 100kHz ring wave as per [3].

Fig. 11. Simulated waveform of 100kHz ring wave.

inactive during the open circuit condition, however, assumes importance in shaping the short circuit current in case of hybrid wave generator. This resistor would be seen as a part of the source impedance of the surge generator. The specially designed and fabricated surge generators are presented in Fig. 12 and Fig.13 which can generate ring wave and combination wave as per [1-5].

B. Instrumentation used for the study The voltage and current measurements are monitored using a Rigol make DS1042C, 2-channel, 40MHz, 400MSa/s digital storage oscilloscope. For voltage measurement a resistive (non-inductive) voltage divider of ratio: 50 is employed to bring down the voltage to safe measurable range of oscilloscope. Pearson current monitor Model 1025 is employed for the measurement of current. The output voltage of CT is to be multiplied by 1/0.025 = 40 for obtaining the actual current.

C. Experimental Results and Analysis Experimental investigations were carried on two types of high voltage high current protection cards containing 8-ports and 24 ports used in protection of digital telephone exchanges. These protection cards were evaluated for both ring waves and combination waves. The performance of these cards for different terminal combinations like TIP (T) and ground, Ring(R) and ground, Tip-Ring and ground and between Tip and Ring were evaluated for voltage magnitudes ranging from 1kV to 5kV respectively. At least five pulses were applied for each terminal port of the HVP cards. The typical waveforms recorded and the comparison of the performance for the 8-port and 24 port HVP cards for voltage magnitudes of 5kV in case of combination wave are given in Fig. 14 to Fig.21 and for ring

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Fig. 12. Experimental arrangement with fabricated ring wave generator.

Fig. 13. Experimental arrangement with Combination wave generator.

Fig. 14. 5kV combination wave pulses applied to 8-port HVP card (T-R).

wave applications are presented in Fig. 22 to Fig. 29 respectively. The experimental results obtained for the performance of each port are analyzed for different peak voltage magnitudes. The comparative results for both combination waves and ring wave applications for 4kV and 5kV magnitudes are shown in Fig.30 for 8-port and Fig.31 for 24-port protection card.

Fig. 15. 5kV combination wave pulses applied to 8-port HVP card(T-G).

Fig. 16. 5kV combination wave pulses applied to 8-port HVP card(R-G).

Fig. 17. 5kV combination wave pulses applied to 8-port HVP card(TR-G).

Fig. 18. 5kV combination wave pulses applied to 24-port HVP card(T-G).

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Fig. 19. 5kV combination wave pulses applied to 24-port HVP card(R-G).

Fig. 20. 5kV combination wave pulses applied to 24-port HVP card(TR-G).

Fig. 21. 5kV combination wave pulses applied to 24-port HVP card(T-R).

Fig. 22. 5kV Ring wave pulses applied to 8-port HVP card(T-R).

Fig. 23. 5kV Ring wave pulses applied to 8-port HVP card(T-G).

Fig. 24. 5kV Ring wave pulses applied to 8-port HVP card(R-G).

Fig. 25. 5kV Ring wave pulses applied to 8-port HVP card(TR-G).

Fig. 26. 5kV Ring wave pulses applied to 24-port HVP card(TR-G).

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Fig. 27. 5kV Ring wave pulses applied to 24-port HVP card(T-R).

Fig. 28. 5kV Ring wave pulses applied to 8-port HVP card(T-G).

Fig. 29. 5kV Ring wave pulses applied to 8-port HVP card(R-G).

Fig. 30. Comparison of peak voltage magnitudes for 8-port card

The results of the performance of HVP cards for both ring wave and combination waves indicate, the output waveforms with the protection card show a reduction in magnitude and time. A physical verification of these cards was also done to check the changes if any, before after voltage application. A relative comparison of these cards cannot be made because of the components used in these cards differ each other.

Fig. 31. Comparison of peak voltage magnitudes for 24-port card

IV. SUMMARY AND CONCLUSIONS In the absence of commercial generators in the market

for evaluation of telecom equipment, special efforts were made to fabricate both the ring wave and hybrid/ combination wave surge generators. The fabricated surge generators meet the requirement of prescribed standards and are capable of delivering an output of 0.5µs-100kHz Ring wave and 1.2/50µs and 8/20µs in case of combination wave used for testing and evaluation of telecom modules.

Two types of telecom protection cards of 8-port and 24-port are subjected to surge voltage magnitudes of 1kV to 5kV, results obtained for both combination wave and ring wave pulses are analyzed and presented.

The performance of HVP cards during and after application of surges was monitored for different ports for lightning protection adequacy.

ACKNOWLEDGMENT The authors would like to thank Prof Udaya Kumar, Dept.

of EE, IISc, Bangalore and Mr B R Suresh of M/s C-DoT, Bangalore for the help and encouragement.

REFERENCES [1] IEEE Std C62.41.1-2002, "IEEE guide on surge environment in low

voltage ac power circuits", 2002. [2] IEEE Std C62.41.2-2002, "IEEE Recommended practice on

characterization of Surges in low voltage", 2002. [3] IEEE Std C62.45-2002, "IEEE Recommended practice on Surge testing

for equipment connected to low voltage ac power circuits", 2002. [4] ITU-T, K.20-2003, "Protection against interference for

telecommunication equipment", 2003. [5] ITU-T, K.44-2003, "Protection against interference for

telecommunication equipment", 2003. [6] Udaya Kumar and Subba Reddy B, "Lightning compatibility tests on

new generation avionic packages", Technical report No: CP: 6091/0403/2009/877, CSIC, IISc Bangalore, 2009.

[7] Subba Reddy B and Udaya Kumar, "Performance evaluation of CDOT developed HVP cards used in RAX/MAX systems subscriber lines", Technical report No: 6107/0403/2009, CSIC-IISc, Bangalore, 2009.

[8] Subba Reddy B and Udaya Kumar, “A Hybrid Impulse Generator”, Journal of Instrument Society of India. Vol.41, No:3, pp 155-157, 2011.

[9] Subba Reddy B and Udaya Kumar, “Performance of Telecommunication Modules to 0.5µs-100kHz Ring Wave Surges”, IEEE-ICPADM held at CPRI, Bangalore. Paper ID: 194, July 2012.

[10] Aristide Torrelli and Spyros Pappas, “An update on power line surge protection techniques for telecommunication facilities”, Paper no: 28-2, ieee explore: 978-1-4244-2056-8/08/$25.00©2008 IEEE.

[11] Janklovics, “The place and role of power supply in the overvoltage protection and risk assessment damages to telecommunication sites due to lightning discharges”, International telecommunications energy special conference, Budapest, Hungary, pp 439-446 , April 1997.