EMP Effects on Protection and
Control Systems
Copyright © SEL 2014
Overview
• EMP description and effects on protection and
control systems
• EMP standards for C4 buildings
• Present EMC standards and protection for
protection and control systems
♦
♦
♦
Relays and IEDs in general
Panels and Control Houses
Cables
• Possible changes to present design for better
EMP protection
• Testing requirements and preliminary results
EMP Threat
• High Altitude Electromagnetic Pulse (HEMP)
♦
Nuclear burst,
very high altitude
(>30km, effects
known since 60’s
experiments
>400km)
• High Power Microwave (HMP) or Intentional
Electromagnetic Interference (IEMI)
♦
Non-explosive weapons, repeatable pulses
directed by antennas, much smaller intensity
and area
EMP Effects and Waveforms
• Strong Electric and Magnetic Fields
• Voltages and currents induced on metallic
conductors
• Possible disruption or damage to electric or
electronic equipment
• Simultaneous
effects over wide
area
EMP Effects on Substation Control
Houses, Panels and IEDs
• Similar to harsh electromagnetic events and
environments found in power systems
Lighting strikes, RFI, HV surge events, strong magnetic
fields during short circuits, etc.
• Possibly higher severity and different
frequencies
E1 may affect IEDs at the circuit board level and couple
with shorter conductors (1- 10m), E2 and E3 affects
longer conductors and lines (km, several seconds).
Biggest concern conductors from substation yard to
control building
EMP Protection at IED Level
• Power systems protection
and control standards for
IEDs are much more
robust than commercial or
even industrial equipment.
• Specify highest severity
levels listed in present
standards
• Select products that have
been designed to exceed
these standards
SEL-311C Tested at US Army’s
Picatinny Arsenal in New Jersey
• RF from 100 MHz to 4 GHz at power levels from 25 to
1000 volts per meter (Mil-Std 461 ask for 50V/m only)
SEL-311C at US Army’s Picatinny
SEL-311C at US Army’s Picatinny
SEL-311C Analog Measurements During IEMI
In Tolerance
Out of Tolerance
1100
1000
900
Field Strength (V/m)
800
700
600
500
400
300
200
100
0
100
175
500
920
1000
1500
2000
2400
3000
3500
4000
Frequency (MHz)
• No damage, out of tolerance may not lead to relay
missoperations if applied with best engineering
practices
EMP Standards
• Military standards
♦
MIL-STD-188-125A 1998 High Altitude
Electromagnetic Pulse Protection for Ground-Base
C4I Facilities Performing Critical Time-Urgent
Missions
• IEC SC 77C
EMP Hardening / Enclosure
• Facility shield / Electromagnetic barrier
♦
Faraday Cage: Metallic continuous conductive
enclosure closed on all wall, ceiling and floor.
♦
Continuously welded, qualified procedures and
personal
♦
Minimize points of entry (POEs)
♦
Equipotential ground plane
Control Houses and Systems for EMP
• SEL has not designed EMP shielded control
houses
♦
No utility customer requirements
♦
IEC standards recently released
• Present control house design and IED
technologies already hardened vs. other types
of electromagnetic effects
• Major design changes would be required to
meet HEMP standards
• Test and validation needs special equipment
Present Control Houses Shield
• Several control house designs provide external
metallic shield
Present Control Houses Shield
• Sometimes provide 2 or 3 metallic barriers that
attenuate electromagnetic fields (not welded)
Control Houses Hardened Shield for
EMP Military Std-188-125A.
• Faraday Cage Inside Metal or Concrete Power Core
• Change of steel gauge and continuously welded
EMP Hardening / Enclosure
• Protection and Control Panels
♦
Closed cabinets provide extra shielding for IEDs
EMP Hardening / POEs
• Architectural entryways, two shielded doors,
interlocks (or unprotected when open). No
windows.
• Mechanical POE like piping and ventilation
• Waveguide-below-cutoff
EMP Electrical POEs
• Main threat to substation control rooms,
coupling at conductors to yard
• Each power, communication and control
conductor (shielded or unshielded) shall be
provided with transient suppression /
attenuation devices
♦
Surge arresters, filters, non-linear elements, etc
• Exceptions for conductors on specific
conditions of conduit shielding
♦
1-10Amp, 250m (820ft) buried metallic conduit or
31m (102ft) non-buried metallic conduit
Cable Entry Protection
• Mil – Std 188
Control Houses POEs
• Modify vents to waveguide-below-cut-off
• Shielded doors
• Each conductor protected or each conduit shall be
welded to shield
• Limit number of control conductors entering control
building from substation yard
Cable Entry Protection
Individual Cable EMC protection
Transmission Yard Conductors
Minimize Electrical Points of Entry
Using Fiber Optics
• Peer to peer technologies available
♦
Serial Mirrored Bits / Ethernet GOOSE
♦
Process Bus Technologies under development for analog
signals (CTs & PTs)
• Reduce commissioning or substation upgrade time,
copper cost, cable trench cost and size and POEs
• Avoid cable or conduit protection and Current Pulse
Injection Test
• Increase fiber and field cabinet cost, cabinet must be
totally closed (NEMA 4) and hardened for EMP with
EMC gaskets
Hard Wire Process Bus
72 CC for analog inputs
60 CC for discrete inputs
Traditional injection testing
Fiber Process Bus
7 fiber for analog/discrete or
Process bus optional, relays
in FTK wired to each CT/PT
Traditional injection testing
Remote I/O Near Breakers and
Transformers
Shielding Effectiveness Test
Pulse Current Injection Test
Cable Entry Protection
Testing for conducted current
Preliminary Testing to Control House
• Test with control house “as is”
♦
Only shielding effectiveness test
♦
30 to 40dB average attenuation
from 10kHz to 10GHz
♦
Conventional doors, cable entries
and louvers are the main leakage.
10 to 20db attenuation
Summary
• Understand customer requirements for EMP, review
standards for utility applications
• Use substation hardened IEDs for relays, controls
and HMI computers
• Reduce electrical POEs with fiber optics to reduce
yard conduits and their welded connections to control
house or individual cable protections
• Significant costs associated with manufacturing a
control building with integrated faraday cage.
• Specialized test procedure and equipment for MIL
standard compliance would be required.