Surge Mitigation Component Overview

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1 Surge Mitigation Component Overview Presented by Mick Maytum

2 Protection or Mitigation? Protective: having the quality or character of protecting; tending to protect; defensive; preservative. Because of history we are going to be stuck with using the word protective. Protective is a system, not a component or device, property that depends on not only the component or device functions but also the surge and the downstream circuit withstand. To say the protective function protects in all circumstances is generally not true. In the test laboratory with a defined surge and with a defined protected item withstand one can say protection is achieved. By itself a protective function can be said to mitigate (reduce) a surge. Even then some load condition is implied such as an open-circuit for a voltage limiting protective function or a short-circuit for current limiting protective function. For a standalone surge protective function situation, the word mitigation (the action of reducing the severity, seriousness, or painfulness of something) is a more appropriate word than protective. Mitigation can achieved by either surge restriction (e.g. clamping) or surge reducing (e.g switching or attenuation). 2

3 What is a surge? IEC non-periodic and relatively short positive or negative (or both) variable (voltage or current) between two steady states - IEC transient wave of electrical current, voltage, or power propagating along a line or a circuit and characterized by a rapid increase followed by a slower decrease - IEC transient created by LEMP (lightning electromagnetic impulse) that appears as an overvoltage and/or an overcurrent - IEC

4 What is a surge? ITU-T Temporary excessive voltage or current, or both, coupled on a telecommunication line from an external electrical source - ITU-T K.46, ITU- T K.89 Overvoltage and/or overcurrent of a transient nature that may be imposed on a conductor as a consequence of an electromagnetic disturbance - K.46 Temporary excessive voltage or current, or both, coupled on a telecommunication line, from an external electrical source - K.65 4

5 What is a surge? IEEE A transient voltage or current, which usually rises rapidly to a peak value and then falls more slowly to zero, occurring in electrical equipment or networks in service - IEEE Std 4 A transient wave of current, potential, or power in an electric circuit - IEEE Std C62.11 A transient wave of voltage or current. The duration of a surge is not tightly specified, but it is usually less than a few milliseconds - IEEE Std C62.34 An impulse, occurring in electrical equipment or networks in service - IEEE Std

6 What is a surge? Conclusion The ITU (Telecommunications) only classifies an electrical disturbance as a surge when the amplitude is an overvoltage or overcurrent or both. The surge is not defined in terms of waveshape or duration. The IEEE is more pedantic on the waveshape and timings without defining amplitude. It completely misses the situation of a truncated surge which has a relatively slow rise and rapid decay. The IEC only considers short term disturbances. One case considers a disturbance that is only an overvoltage or overcurrent or both and due to lightning. Phases overvoltage and overcurrent are system dependent. For non-linear components these phases relate to voltages or currents that exceeds the component threshold level. A working generic definition for surge can be taken as: surge: temporary disturbance on the conductors of an electrical service caused by an electrical event. 6

7 Surge Protection Functions Surge Mitigation Functions Limiting Non-linear Attenuating Linear Overvoltages Overcurrents Frequency selective Continuous Characteristic Discontinuous Characteristic Continuous Characteristic Discontinuous Characteristic Low-pass Band-pass High-pass Transformer Action Isolating Neutralising Choke 7

8 Limiting Non-linear Limiter: non-linear function that automatically restricts the amplitude of a given quantity when it exceeds a predetermined threshold level for more than a given time Re-entrant Foldback Switching Transitions Threshold Continuous Characteristic - Clamping Threshold Discontinuous Characteristic - Switching 8

9 Voltage Limiter Clamping Punch-Through Diode, NPN or PNP structure 2 V to 4 V threshold, Base region fully occupied by depletion layer and punches through to the emitter region Zener Breakdown Diode, PN structure 3 V to 6 V threshold, Zener Effect Avalanche Breakdown Diode, PN structure 8 V and above threshold, Avalanche effect Foldback Diode, NPN or PNP structure 8 V and above, Avalanche effect and transistor V CBO to V CEO transition 9

10 Voltage Limiter Switching Gas Discharge Tube (GDT), two or three electrode 75 V to over 6000 V threshold Thyristor, PNPN structure 12 V to over 800 V threshold, Fixed voltage, Avalanche breakdown triggered, unidirectional and bidirectional thyristors Gated, N-gate, P-gate or both, referenced or triggered. 10

11 Current Limiter Clamping Re-Entrant Ceramic Positive Temperature Coefficient Thermistor Re-Entrant Polymer Positive Temperature Coefficient Thermistor Current Source Electronic Current Limiter Re-Entrant Electronic Current Limiter 11

12 Shunt gated-triggered thyristor Current Limiter Switching 12

13 Linear Attenuating Filters Low-Pass Lightning spectrum above service frequency Band-Pass Lightning spectrum different to service frequency, example quarter-wave stub High-Pass Lightning spectrum below service frequency 13

14 Attenuating Linear Transformers Neutralising Used to buck out the power frequency ground potential rise differences between separated grounds on the communication line. The neutralising transformer can also buck out magnetically induced voltages on the communication line. The transformer consists of closely coupled windings on a ferromagnetic core. The transformer primary winding is connected between the remote grounds. A secondary winding is placed in series with each conductor of the communications wire line pair. The GPR voltage difference is applied to the transformer primary. The secondary windings, in series with the communications lines, are connected in anti-phase so their transformed voltage opposes the GPR voltage difference. Ideally the communication line transformed voltage and the GPR voltage difference cancel out, neutralising the GPR voltage difference. 14

15 Attenuating Linear Transformers Isolating These in-line transformers have a protective separation between the input and output windings. This galvanic break attenuates common-mode (longitudinal) surges. Differential signals and surges are transformed from one winding to the other. lightning isolation transformer: shunt in-line transformer used to mitigate common-mode voltage without affecting differential voltage. 15

16 Attenuating Linear Transformers EMC choke These are two winding transformers. For a twisted pair each winding is placed in series with a conductor and poled to give a transformer action that presents high impedance to common-mode signals and low impedance to the wanted differential signal. Coaxial cables can be wrapped round a magnetic core to give the same effect. common-mode choke/filter: series in-line transformer used to mitigate common-mode current flow without affecting differential current flow. 16

Distribution Transformer Random Transient Suppression using Diode Bridge T-type LC Reactor

Distribution Transformer Random Transient Suppression using Diode Bridge T-type LC Reactor Leong Bee Keoh 1, Mohd Wazir Mustafa 1, Sazali P. Abdul Karim 2, 1 University of Technology Malaysia, Power Department,