Download Overvoltage and Overcurrent Protection Component Overview

Surge Mitigation Component
Overview
Presented by Mick Maytum
[email protected]
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Surge Protection 101 - Part 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).
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Surge Protection 101 - Part 2
What is a surge? IEC
non-periodic and relatively short positive or negative (or both) variable (voltage
or current) between two steady states - IEC 60571
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 61000-4-5
transient created by LEMP (lightning electromagnetic impulse) that appears as an
overvoltage and/or an overcurrent - IEC 62305-1
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Surge Protection 101 - Part 2
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, ITUT 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
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Surge Protection 101 - Part 2
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
1783
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Surge Protection 101 - Part 2
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.
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Surge Protection 101 - Part 2
Surge “Protection” Functions
Surge Mitigation Functions
Limiting Non-linear
Attenuating Linear
Overvoltages
Continuous
Characteristic
Overcurrents
Discontinuous
Characteristic
Continuous
Characteristic
Frequency selective
Discontinuous
Characteristic
Low-pass
Band-pass
High-pass
Transformer Action
Isolating
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Neutralising
Choke
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Surge Protection 101 - Part 2
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
Threshold
Continuous Characteristic - Clamping
Discontinuous Characteristic - Switching
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Surge Protection 101 - Part 2
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 VCBO to VCEO transition
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Surge Protection 101 - Part 2
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.
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Surge Protection 101 - Part 2
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
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Surge Protection 101 - Part 2
Current Limiter
Switching
Shunt gated-triggered thyristor
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Surge Protection 101 - Part 2
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
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Surge Protection 101 - Part 2
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.
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Surge Protection 101 - Part 2
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.
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Surge Protection 101 - Part 2
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.
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Surge Protection 101 - Part 2