Part 2: Protection & Communication
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- 📍 Part 2: Cubicle Details and Protection (this page)
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Item 1 - Incoming Feeder Cubicle
The 22 kV Incoming Feeder Cubicle shall comprise the following basic equipment:
| Qty | Equipment/Description |
|---|---|
| 1 | Three-phase 630 A busbar |
| 1 | Motorised load break switch disconnector of rating 630A and housed in SF6/ Vacuum filled enclosure having padlocking facilities. |
| 1 | Motor operated spring charged operating mechanism for quick closing and opening independent of the operator. Manual spring charged operating mechanism should also be provided in case of failure of motor. |
| 1 | Earthing switch located in such a position to allow its contacts to be seen easily through the cubicle window |
| 1 | Mechanical interlocking system between disconnector and earthing switch |
| 1 | Neon lamp for live cable indication |
| 1 | Cable compartment with cable terminations for the reception of 3-core aluminium 240 mm² or copper 300 mm² XLPE cable to IEC 60502-2. The cable entry is to be at the front of the panel |
| 1 | Bottom plate with cable gland |
| 1 | Built-in padlocking device of the cubicle door |
The front facia should be equipped with appropriate padlocking facilities that will allow the operator to lock the disconnector switch and earth switch in close/open position independently.
The incoming 3-Core power cable shall be centered below the Panel Base / Bottom Plate and cable terminations (Indoor) shall be mounted inside the MV compartment of the incomer switchgear panel (refer to drawing 6640-18). Rubber Bushings shall be provided for sleeve protection for cable of size ranging from 65mm to 100mm.
The load break switch disconnector shall have both local and remote modes of operation via a key selector switch which should be mounted on the front facia. The key should be released in local mode only.
Guaranteed Particulars
The Client shall also supply all relevant data where applicable by filling in the Schedule of Guaranteed Particulars - Schedule B2.
Item 2 - Voltage Transformer Cubicle
The 22 kV Voltage Transformer Cubicle shall comprise the following basic equipment:
| Qty | Equipment/Description |
|---|---|
| 1 | Three-phase 630 A busbar |
| 1 | Triple pole isolator |
| 1 | Manual operating mechanism |
| 3 | HRC fuses to DIN specifications rated to suit VT's rating Note: Access to the fuses shall only be possible with the switch in the "Earth" position in such a way that both sides of the fuse are effectively earthed. |
| 1 | Auxiliary switch connected to the VT secondaries and opening with the 22 kV isolator to prevent feedback from the LV side. |
| 3 | Single phase voltage transformers |
| 2 | Secondary windings. Each PT shall be equipped with 2 windings: one winding to be used for metering and the second winding for open delta protection. |
Voltage Transformer Specifications:
Metering core
- Ratio: 22,000 V / √3 : 110 V / √3
- Rated burden: minimum of 10 VA
- Accuracy Class: CL 0.5
Protection core
- Ratio: 22,000 V / √3 : 110 V / √3 or 110V / 3
- Rated burden: minimum 15VA
- Accuracy Class: 3P
| Qty | Equipment/Description |
|---|---|
| 1 | LV fuse box containing 3 LV fuses of appropriate rating + 3 neutral links |
| 1 | Built-in padlocking facility on the cubicle door |
The system shall be designed and implemented to prevent or damp any ferroresonance effect in the PTs.
As mentioned above, the burden for the PTs (metering) shall be minimum 10VA. However, the Client's Electrical Engineer shall provide the burden calculation for the instrumentation transformers so as to ensure that the proposed PTs are rated correctly and they are operating within the optimum range (i.e. between 0% and 100% of the rated burden). It can be assumed that the maximum burden for the meter is 3VA per phase and secondly, the supervisory cable used is 1.5 mm² Copper cable.
The front facia should be equipped with appropriate padlocking facilities that will allow the operator to lock the disconnector switch and earth switch in close/open position independently.
Guaranteed Particulars
The Client shall also supply all relevant data where applicable by filling in the Schedule of Guaranteed Particulars - Schedule B3.
Item 3 - CEB Circuit Breaker Cubicle
The 22 kV Circuit Breaker Cubicle shall be of double isolation and comprise the following basic equipment:
| Qty | Equipment/Description |
|---|---|
| 1 | Three-phase 630 A busbar |
| 2 | Triple pole isolator |
| 1 | SF6 Gas/ Vacuum Circuit Breaker |
| 1 | Motor operated spring charged operating mechanism for quick closing and opening both locally by push button and remotely. |
| 1 | Tripping coil 230 V ac for emergency tripping |
| 1 | Trip release device to work in conjunction with the relay mentioned below in Schedule A2. |
| 3 | Current transformers with dual primaries e.g. 100/200 or 200/400 rated amp with secondaries of 5A, Class 5P20, 10VA burden for protection and 5A Class 0.5, minimum of 10 VA burden for metering. The minimum primary current shall be 100A to prevent any saturation of the CT during a fault condition. |
| 1 | Voltage test terminal block |
| 1 | Current test terminal block |
| 2 | Tripping test terminal block |
| 1 | Mechanical interlocking between earthing switch and triple pole isolator |
| 1 | Earthing switch located in a position to allow its contacts or position to be seen easily through the cubicle window |
| 1 | Bottom plate with cable gland |
| 1 | Neon lamp for live cable indication |
| 1 | Built-in padlocking device for the cubicle door |
As mentioned above, the burden for the CTs (metering) shall be minimum 10VA. However, the Client's Electrical Engineer, shall provide the burden calculation for the instrumentation transformers so as to ensure that the proposed CTs are rated correctly and these are operating within the optimum range (i.e. between 25% and 100% of the rated burden). It can be assumed that the burden for the meter is 0.1VA per phase and the supervisory cable used is 2.5 mm² Copper cable.
The Circuit Breaker shall have both local and remote modes of operation via a key selector switch which should be mounted on the front facia. The key should be released in local mode only.
The front facia should be equipped with appropriate padlocking facilities that will allow the operator to lock the disconnector switch and earth switch in close/open position independently.
Important Notes:
- Toroidal CTs WILL NOT BE ACCEPTED for metering purposes.
- CT ratio will depend on installed load and will have to be specified at the time of order.
- The metering CT shall be mounted so that P1 is located on CEB side direction and P2 on client side direction.
- In addition, an interlocking system shall be provided to ensure that closing of the CEB 22kV Circuit Breaker is ONLY allowed if ALL the Client 22 kV Circuit Breakers are in the open position. The opening of the CEB 22kV Circuit Breaker shall inter trip ALL the Client 22 kV Circuit Breakers. However, this interlocking/ inter-tripping feature shall be enabled only for MSDG, IPPs installations etc.
Guaranteed Particulars
The Client shall also supply all relevant data where applicable by filling in the Schedule of Guaranteed Particulars - Schedule B4.
Item 4 - Outgoing Feeder Cubicle/s (Client's Side)
22 kV circuit breaker(s) shall be required on the outgoing feeder panel(s) on Client's Side.
Schedule A2 - MULTIFUNCTIONAL PROGRAMMABLE NUMERICAL PROTECTION RELAYS
The Programmable Protection Relays shall include at least Overcurrent, Earth Fault and Neutral Voltage Displacement (NVD) protections and shall operate with the secured auxiliary supply, with independent time settings for each type of protection as detailed hereunder:
The numerical relay shall comprise of two or more low set stages and one high set stage for both overcurrent and earth fault protection.
Low set overcurrent and earth fault elements must consist of both Inverse Definite Minimum Time (IDMT) and Definite Time Stages. Relay must also provide both delayed and instantaneous overcurrent and earth fault high set elements.
(a) The primary range of overcurrent protection should be as follows:
1. Low Set (I>):
- At Inverse time: 15 Amp to 400 Amp with time multiplier range: 0.05 to 1.5
2. High set (I>>):
- At definite time or instantaneous stage: 200Amp to 2000 Amp with time range of 0s to 20s DT.
(b) The primary ranges for the earth fault elements should be as follows:
1. Low Set (I>):
- At Inverse time: 10 Amp to 100 Amp with time multiplier range: 0.05 to 1.5
2. High set (I>>):
- At definite time: 50 Amp to 1500 Amp with time range of 0s to 20s.
The typical range of overcurrent is based on an installation capacity of 500kVA to 10MVA. In case, the capacity is outside the above range the overcurrent setting might be inappropriate. It is also assumed that the minimum primary setting of the CT is set on 100A to prevent saturation of the CT during a fault.
The supplier shall select the appropriate protective relay based on the above primary ranges.
(c) Neutral Voltage Displacement
- At Definite time: 1…. 20% x (22kV/√3)
- Operating time at Definite time: 0.05 …... 20s
Prior to relay testing, the client's settings proposal for 'CEB side relay' must be verified and approved by CEB. The client is to take responsibility that the 'client's side protection relay' settings grades properly with 'CEB's side relay'. Relay test certificates must be provided.
Any relay settings' changes (if required) is to be carried out by the client and tested accordingly by the client. However, these settings must be vetted by the CEB. The Client shall provide CEB with a PC-to-relay communication cable and the updated relay software.
Note:
- The circuit breaker's main function is for protecting Central Electricity Board's system from client's system against faults on client's side and not for transformer protection. Client shall therefore provide for a transformer protection panel for each transformer.
- The Client shall make provision for the training of CEB personnel on the configuration and operation of the relays.
- All protection relays shall have test blocks for current, voltage and tripping. Client to provide CEB with pre-wired plugs for each test block.
- The Neutral Voltage Displacement protection shall be enabled only for MSDG and IPPs clients.
- Alarms should be communicated to CEB SCADA to signal any loss of supply to and from the UPS.
- Client shall be responsible for providing the CEB with a study report complete with curves illustrating co-ordination between new and existing systems along with all calculations to determine relay settings.
- The Client shall submit a hard copy as well as a soft copy of the relay configuration, settings and manuals (if required by the CEB) before commissioning.
- Multi-function protection shall have the functions indicated on the electrical schematic/specification drawings.