Document Number: EDS 05-0001D

UK POWER NETWORKS ENGINEERING DESIGN STANDARD - EDS 05-0001D APPENDIX D Version: 6.0
132KV, GRID AND PRIMARY SYSTEM PROTECTION AND CONTROL SCHEMES Date: 19/10/2015
CT Schedule for Protection and Control Schemes in UKPN EDS 05-0001D v6.0

132kV Busbar Substation

Protection Scheme CT Ratio CT Ratio CT Ratio CT Class CT Rating Notes Updated
Bus Section

Bus Zone (Main) 1/1000/2000 - - Class PX Vk > 95(Rs + 2.5) See Notes 3, 4 & 23 10/19/2015

Bus Zone (Check) 1/1000/2000 - - Class PX Vk > 95(Rs + 2.5) See Notes 3, 4 & 23 10/19/2015
Instruments 1200/600/1 - - 5P20 & Class 1 15VA See Note 4

Bus Coupler
Bus Zone (Main) 1/1000/2000 - - Class PX Vk > 95(Rs + 2.5) See Notes 3, 4 & 23 10/19/2015
Instruments 1200/600/1 - - 5P10 & Class 1 15VA See Note 4

Feeder
Main Protection 1/500/1000 - - Class PX Vk > 60(Rs +12) See Notes 5 & 23 1/22/2009
Main Protection (Special Applications) 1/600/1200 - - Class PX Vk > 50(Rs +17) See Notes 5 & 23 1/22/2009
See Note 5
Back up Protection 1200/600/1 - - 5P20 & Class 1 15VA
See Note 6
Instruments 1200/600/1 - - 5P20 & Class 1 15VA See Note 6
Bus Zone (Check) 1/1000/2000 - - Class PX Vk > 95(Rs + 2.5) See Notes 7 & 23 10/19/2015
Bus Zone (Main) 1/1000/2000 - - Class PX Vk > 95(Rs + 2.5) See Notes 7 & 23 10/19/2015

132/33kV Substation
Protection Scheme CT Ratio CT Ratio CT Ratio CT Class CT Rating Notes Updated
Starting from the terminal end
Transformer 132kV Bushings 90MVA 60MVA 45MVA
Main Protection 1/500 1/350 1/200 Class PX Vk = 35(Rs + 5)
Back-up Protection 500/1 400/1 300/1 5P20 & Class 1
Feeder Back-up Protection 1200/600/1 1200/600/1 1200/600/1 5P20 & Class 1 15VA
Main Protection 1/500/1000 1/500/1000 1/500/1000 Class PX Vk > 60(Rs +12) See Note 23 7/6/2009
Main Protection (Special Applications) 1/600/1200 1/600/1200 1/600/1200 Class PX Vk > 50(Rs +17) See Note 23 7/6/2009

132kV Neutral
Restricted Earth Fault 1/500 1/350 1/200 Class PX Vk = 35(Rs + 5)
Spare CT 500/1 500/1 500/1 5P20 & Class 1 15VA

Earthing Transformer Neutral

Standby Earth Fault 1600/800/1 5P20 & Class 1 15VA See Note 8
Restricted Earth Fault 1/2000 1/1200 1/1200 Class PX Vk = 35(Rs + 5)

33kV Switchgear (Incomer)

Rough Balance Busbar Protection. 2000/1 2000/1200/1 2000/1200/1 5P20 & Class 1 15VA See Note 9
Instruments 2000/1 2000/1200/1 2000/1200/1 5P20 & Class 1 15VA See Note 9
See Note 9
Directional Overcurrent 2000/1 2000/1200/1 2000/1200/1 5P20 & Class 1 15VA
See Note 10

Page 1 of 4
 Document Number: EDS 05-0001D
UK POWER NETWORKS ENGINEERING DESIGN STANDARD - EDS 05-0001D APPENDIX D Version: 6.0
132KV, GRID AND PRIMARY SYSTEM PROTECTION AND CONTROL SCHEMES Date: 19/10/2015
See Note 9
Biased Differential 1/2000 1/1200/2000 1/1200/2000 Class PX Vk = 35(Rs + 5)
See Note 10

33kV Switchgear (BS or BC)

Rough Balance Busbar Protection. 2000/1 2000/1200/1 2000/1200/1 5P20 & Class 1 15VA See Note 9
Rough Balance Busbar Protection. 2000/1 2000/1200/1 2000/1200/1 5P20 & Class 1 15VA See Note 9
Instruments 2000/1 2000/1200/1 2000/1200/1 5P20 & Class 1 15VA See Note 9

132/11/11kV Substation
Protection Scheme CT Ratio CT Ratio CT Ratio CT Class CT Rating Notes Updated
Starting from the terminal end
Transformer 132kV Bushings 60MVA - -
Main Protection 1/350 - - Class PX Vk = 35(Rs + 5)
Back-up Protection 1/350 - - Class PX Vk = 35(Rs + 5)
Feeder Back-up Protection 1200/600/1 - - 5P20 & Class 1 15VA
Main Protection 1/500/1000 1/500/1000 1/500/1000 Class PX Vk > 60(Rs +12) See Note 23 7/6/2009
Main Protection (Special Applications) 1/600/1200 1/600/1200 1/600/1200 Class PX Vk > 50(Rs +17) See Note 23 7/6/2009

132kV Neutral
Restricted Earth Fault 1/350 - - Class PX Vk = 35(Rs + 5)
Spare CT 500/1 - - 5P20 & Class 1 15VA

Earthing Transformer Neutral

Standby Earth Fault 800/1 - - 5P10 15VA See Note 11
Restricted Earth Fault 1/2000 - - Class PX Vk = 35(Rs + 5)
- -
11kV Neutral - Star/Star Transformer - -
See Note 11
Standby Earth Fault 800/1 - - 5P20 & Class 1 15VA
See Note 12
Restricted Earth Fault 1/2000 - - Class PX Vk = 35(Rs + 5) See Note 12
11kV Neutral Earth Fault Alarm 1000/5 - - 5P10 15VA Se Note 18

11kV Switchgear (Incomer)

Rough Balance Busbar Protection 2000/1 - - 5P20 & Class 1 15VA
Directional OC & Instruments 2000/1 - - 5P20 & Class 1 15VA
Biased Differential (Back-up) 1/2000 - - Class PX Vk = 35(Rs + 5)
Biased Differential (Main) 1/2000 - - Class PX Vk = 35(Rs + 5) See Note 13

11kV Switchgear (BS or BC)

Rough Balance Busbar Protection 2000/1 - - 5P20 & Class 1 15VA See Note 14
Rough Balance Busbar Protection 2000/1 - - 5P20 & Class 1 15VA

As 33/11kV
11kV Feeders
substation

Page 2 of 4
 Document Number: EDS 05-0001D
UK POWER NETWORKS ENGINEERING DESIGN STANDARD - EDS 05-0001D APPENDIX D Version: 6.0
132KV, GRID AND PRIMARY SYSTEM PROTECTION AND CONTROL SCHEMES Date: 19/10/2015
33kV Busbar Substation
Protection Scheme CT Ratio CT Ratio CT Ratio CT Class CT Rating Notes Updated
Bus Section See Note 15
Bus Coupler See Note 15

Feeder See Note 16

Main Protection 1/800 - - Class PX Vk = 35(Rs + 5) See note 17
Back up Protection & Instruments 800/1 - - 5P20 & Class 1 15VA

33/11kV Substation
Protection Scheme CT Ratio CT Ratio CT Ratio CT Class CT Rating Notes Updated
Starting from the terminal end
Transformer 33kV Bushings 20/40 MVA 12/24 MVA 7.5/15 MVA
Main Protection 1/800 1/500 1/300 Class PX Vk = 35(Rs + 5)
Balanced Earth Fault
Back-up Protection 800/1 500/1 300/1 5P20 & Class 1
Vk = 100, Rs = 1.5
Restricted Earth Fault Protection 5/2000 5/2000 5/2000 Class PX Rated primary See Note 22 9/9/2008
current as CB

11kV Neutral
See Note 11
Standby Earth Fault 400/5/1 400/5/1 400/5/1 5P20 & Class 1 10VA 9/9/2008
See Note 12
Vk = 100, Rs = 1.5
Restricted Earth Fault Protection 5/2000 5/2000 5/2000 Class PX Rated primary See Note 22 9/9/2008
current as CB
11kV Neutral Earth Fault Alarm

11kV Switchgear (Incomer)

2000/1 2000/1200/1 2000/1200/1 5P20 & Class 1 15VA
Rough Balance Busbar Protection
2000/1=15VA See Note 19 9/9/2008
(See Note 19) 2000/1 2000/1200/1 2000/1200/1 5P20 & Class 1
1200/1=10VA
Directional OC & Instruments 2000/1 2000/1200/1 2000/1200/1 5P20 & Class 1 15VA See Note 19

11kV Switchgear (BS or BC)

Rough Balance Busbar Protection 2000/1 2000/1200/1 2000/1200/1 5P20 & Class 1 15VA See Note 14
Rough Balance Busbar Protection 2000/1 2000/1200/1 2000/1200/1 5P20 & Class 1 15VA See Note 19

11kV Feeder See Note 20

1/600 - - Class PX Vk = 35(Rs + 5)
(Min Vk 55/41V.
Unit Protection (See Note 21) Max Rs 0.18/0.14Ω See Note 21 9/9/2008
(5/300/400) - - Class PX
including
connections)
Overcurrent and Earth Fault 600/1 - - 5P20 & Class 1 15VA

Page 3 of 4
Notes
1 The specification for 132kV Switchgear requires that CTs have a thermal rating no less that the rating of the circuit breaker and preferably 120% of
this value.
In the case of transformer mounted CTs, the thermal rating shall be at least 130% of the transformr nameplate rating.
2 On Class PX CTs the magnetising current at half the knee point voltage shall not exceed 30mA, except 132kV switchgear - see note 23.
3 Required on both sides of circuit breaker. Alternatively two sets required
4 For a new site, where ther is no requirement to interface with existing equipment, 1/1000 turns ratio is sufficient.
5 Ideally possitioned on the bus bar side of the circuit breaker
6 Back-up Protection and Instrument CTs shall only be combined where there is insufficient space for 5 sets of CTs.
7 Ideally positoned on the feeder side of the circuit breaker
8 Where Earth Fault Current is limited to 1000 amps, the plain 800/1 ratio is to be used. The 1600/800/11 ratio is only required in LPN and SPN
areas.
9 2000/1 ratio for 90 MVA units. All CTs to be suitable for ultimate use with a 90MVA transformer. 1200/1 ratio only required where a smaller
transformer is to be installed initially.
10 At outdoor sites, these to be on the busbar side of the CB
11 Where the earth fault current is limited to 750 amps, a 400/1 ratio shall be used.
Where signifcantly higher earth fault currents are allowed, higher ratio CTs can be considered.
12 These CTs may be accommodated in the Neutral Earthing Reactor or Resistor.
13 This CT to be nearest to the bus bars
14 One CT to be located on each side of the circuit breaker whereever possible.
15 Covered under 132/33kV Transformer Stations
16 All Feeder circuit breakers to rated at 800A
17 1/800 ratio to be standard for new equipment. Dual ratio CTs (to include 1/800 ratio) may be specified when there is a need to match existing
remote ends.
18 Neutral Earth Fault Alarm CT is only required on LPN schemes. May be part of the Neutral Earthing Reactor
19 2000/1 ratio for 40 MVA units. All CTs to be suitable for ultimate use with a 40MVA transformer. 1200/1 ratio only required where a smaller
transformer is to be installed initially.
Alternative shown in RED has been accepted for ECLIPSE switchgear and is dictated by space available accomodation.
20 All Feeders to be 630A rating
21 Where unit protection CT's are required the standard ratio shall be 400/300/5 (Class PX) in line with ES 03-6400 Appendix C.
Where schemes are required to interface with existing equipment this ratio and specification may need to be varied as appropriate.
22 Restricted earth fault CTs added missing from original specification. CT details as original EPN switchgear specification.
23 132kV switchgear CTs to have a maximum resistance of 2.4Ω at 75°C, magnetising current at half knee point voltage not to exceed 60mA.