Chapter 3: MSDG Interconnection Requirements (Part 3)

3.9 Uninterruptible Power Supply

The operation of the equipment under Central Electricity Board's responsibility shall require secured AC auxiliary source of supply also protected by surge and lightning devices. An online uninterruptible power supply (UPS) is required and it shall have adequate capacity to ensure that the protection, measurement, control and communication systems operate without interruption for a minimum duration of at least 3 hours after loss of CEB power supply. The Client shall submit the calculations in the determination of the sizing of the UPS. In the event of loss of the secured auxiliary supply, all the Client's 22kV circuit breakers shall be tripped until remedial actions are taken. The UPS system shall be installed on the Client side and be maintained accordingly by the Client. The UPS shall be equipped with a bypass switch/system that will allow continuous operation during maintenance on the UPS.

3.10 Indication, Alarms and Instrumentation

The alarm and trip facilities shall have local indication and, for MSDG equal to or greater than 1 MW, an additional set of potential-free contacts for onward transmission of the alarm/trip signals to the CEB Substation.

For MSDG equal to or greater than 1 MW, it is highly recommended that a local SCADA (System Control and Data Acquisition) system be installed to allow monitoring and control of the MSDG installation.

The following panel instrumentation and other fittings are required in addition to other standard equipment required or implied for the type of panel and scheme functionality:

1. Transducer fed voltmeter, ammeter, MW, MVAr, indicating import and export, and appropriate test blocks for current and voltage circuits.
2. Suitable test facilities shall be provided for the secondary injection of current/relay testing and for any other tests as reasonably required by CEB.

External indicator lamps, for MSDG greater than 200kW, shall be installed to indicate parallel operation of the MSDG facility with CEB distribution network. A lighted red lamp shall indicate parallel operation while a lighted green lamp shall indicate isolated operation.

All required equipment for the above shall be procured, installed, tested, commissioned and maintained by the MSDG owner.

3.11 Communication Requirements

Until the DMS project is implemented by the CEB, the communication requirement for MSDG Facilities shall be as described hereunder. However, once the DMS project is implemented by the CEB the following two conditions shall apply:

1. The communication requirements for all new MSDG Facilities shall be as per Annex 7, Schedule A3.
2. All existing MSDG Facilities shall modify their communication setup to be in line with Annex 7, Schedule A3.

The MSDG owner shall install communication equipment for secured transfer of operating data and protection and control signals via:

• Fiber optics cable as per Annex 9 (section 7.9 of this Grid Code) for MSDG of capacity equal to or greater than 1 MW.

In those cases where the installation of fiber optic cable is not feasible or advisable because of high risk of damaging cane fire below the cable and there is no alternative routing for the fiber optic cable at a reasonable cost, the communication can be based on wireless technologies, subject to approval by the CEB for each particular case.

Applicant shall bear the cost for the installation of communication system from the MSDG plant to the corresponding substation and shall install, test, commission and maintain the system (this includes equipment found in the CEB side of the interconnection facility and in the corresponding CEB 66 kV-to-22 kV substation).

An LV supply (230 V ± 6%) shall be provided by the CEB in the 66 kV-to-22 kV substation. However, given that this LV supply may be subject to unavoidable voltage disturbances and variations, the MSDG Owner shall ensure that all appropriate measures have been catered on his side for the protection of his communication system which may be sensitive to such power quality issues. In addition, the MSDG Owner shall be responsible for the maintenance of the communication equipment at the CEB substation. The CEB's liability shall lie up to the LV supply and shall not bear any liability for damage in the MSDG owner's communication equipment.

Relevant information for the operation of the electrical system will be transmitted in real time to the System Control Centre through the RTU (remote terminal unit) available at the CEB Substation.

Communication Signals

i. One-Way communication from the CEB Substation to the Generation Facility:

• 22kV Circuit breaker status at the CEB substation (open/close)

ii. One-Way communication from the Generation Facility to the CEB Substation:

• Load Break Switch status OPEN for each incomer (if available)
• Load Break Switch status CLOSED for each incomer (if available)
• Circuit Breaker CEB (CB1) Status (open/close)
• Outgoing Circuit Breaker (client side) (CB2) Status (open/close)
• Outgoing Circuit Breaker (client side) (CB4) Status (open/close) (if required)
• Alarms (list of warnings/alarms will be determined at discussion stage with CEB):
  • Protection Operated
  • Protection relay not healthy
  • SF6 Alarm (if available)
  • UPS Alarms
  • Door Alarm (Switchgear room door on CEB side)
  • Inter-tripping signal
  • Remote/Local signal (Circuit Breaker CEB (CB1))
  • Other Alarms (grouped)
• MW, MVAr (at the import/export interface)
• Voltage level of the Generation Facility 22kV Busbar (Any line-to-line voltage)
• Current (at the import/export interface) (Any phase current)

iii. Remote control facilities (for MSDG facility greater than 1MW only):

• Load Break Switch OPEN CTRL command for each incomer (if available)
• Load Break Switch CLOSE CTRL command for each incomer (if available)
• Circuit breaker CEB (CB1) open
• Circuit breaker CEB (CB1) close

iv. Optical Fibre

The Optical fibre shall connect the generation facility and the 22kV feeder's Substation on which the MSDG is interconnected. The applicant shall bear the cost of the procurement, installation and commissioning of the fibre optic link.

v. Wireless Communications

Where wireless communications are used, either as backup communication channel or as replacement of the fibre optic channel wherever authorized, it shall comply with any requirements approved by CEB and in particular with the following minimum characteristics:

• Use the latest 3G/4G/LTE or newer communication technologies for the bands of frequency used in the Republic of Mauritius
• Use Microwave link as main channel and the latest 3G/4G/LTE as backup channel. Should any of the channel fail, switching to the other channel shall be seamless. In addition, SLA of 4 hours (Service Level Agreement) shall be applicable on the communication equipment to cater for their failure and link loss.
• Alternatively, communication equipment/modem having dual SIM slot capability and using latest 3G/4G/LTE can be used. This shall allow to remove carrier dependency and swapping network operators seamlessly if the primary run into trouble.
• Furthermore, all channels using 3G/4G/LTE technology shall deployed and configured in VPN tunnel mode (virtual private network) for increased security.
• Be equipped with at least two routers, each capable of accommodating two SIM cards from different network operators and automatic switching between operators in case of unsuccessful transmission. The two routers shall be set up as one main and one hot standby router. This setup shall ensure equipment and network redundancy.
• Be capable of transmitting data at a rate of at least 85 kbps downloading and 42 kpbs uploading.
• Have a configuration interface protected by password
• Be capable of using VPN tunnels using, at least, technology Open VPN; and
• Be equipped with support autorecovery mechanism.

3.12 Metering

The CEB meter, current transformers (CTs) and voltage transformers (VTs) will have, at least, an accuracy class according to the table below. The CEB meter shall have separate registers for import and export of energy to measure the electrical energy delivered to CEB by the MSDG and the import energy imported by the client's load from the CEB System. All CEB meters installed shall be certified by the meter lab of CEB.

Table 6: Metering Accuracy

Note: For Greenfield projects the metering accuracy class shall be 0.2

The CEB metering circuits shall be totally separate from the MSDG metering circuits. This is to be achieved through cabling directly from the metering current transformers (CTs) and voltage transformers (VTs). CEB shall be fully responsible for the commissioning of the metering circuits associated with CEB Meters, i.e. all pre-commissioning and final commissioning involving cabling and other circuit verification, CT and VT checks and certification, functional testing, as well as meter testing, secondary injection and final documentation.

As regard to the CTs and VTs, the MSDG promoter shall first seek CEB's approval prior to ordering and send same to CEB's Meter Lab Section for tests prior to installation. Toroidal CTs WILL NOT BE ACCEPTED for HT metering purposes.

A second meter, namely the production meter, shall be installed by CEB inside the MSDG installation to measure the energy production of the MSDG generation facility. The power cable should fit in the inner diameter of the CT for the production meter and the CT shall be according to IEC 61869-2. The CTs must have sealing facilities.

In cases where it is not possible to locate the production meter next to the import/export meter, the production meter shall be equipped with a separate modem and SIM card and shall be installed at a convenient location and be easily accessible to CEB officers. The cost of this additional modem and the monthly communication charge shall be charged to the applicant, as well as any faulty metering equipment in the future.

In cases where additional production meters are required due to site specificities, all production meters, including the associated modems, SIM cards and communication charge, shall be charged to the applicant, as well as any faulty metering equipment in the future.

The MSDG promoter shall send the specifications and burden calculations of the proposed CTs and the Test Terminal Block (TTB) to the CEB for approval before procurement. Alternatively, the TTB can also be purchased from CEB. Before installation, the CTs shall be sent to the CEB for testing, which will be chargeable to the applicant.

*: For MSDG installations requiring summation CTs, both the CTs and summation CTs shall be of the same accuracy.

All meters and related equipment (such as CT, TTB, etc.) shall be housed in a secured cabin, as per CEB's requirements.

A metering cabin shall be erected to house the production meter, TTB, CTs and an isolator, as per CEB's requirements.

All metering cabins shall be fitted with a 13A power socket, protected by a 2A circuit breaker and fed from a secured source of supply.

In addition the panel shall also provide space for the accommodation of a digital 3-phase power recorder/monitor with the remote communication capabilities, if required, for power quality analysis, energy management, data transfer and supervisory control needs.

The applicant may install at his own cost a backup meter (Refer to Drawings in Annex 8) capable of recording both the export of electrical energy from Facility to the CEB Interconnection Facilities and the import of electrical energy by the Facility from the CEB Interconnection Facilities.