Three phase power is usually required by large commercial and industrial customers. These customers have a number of options for the supply of three phase power.
1. Purchase and installation of their own transformer and associated high voltage switchgear. In this instance the customer is provided with a high tension (HT) supply and is metered on the high tension side using a Metering Unit and is billed at the Large Power (LP) tariff. The customer retains responsibility for the maintenance of the transformer and associated high voltage switchgear. The basic voltage available to Large Power (LP) customers is normally:
• 11,000 Volts, three phase.
• In some areas the voltage available is 24,900 Volts, three phase.
2. Use of Barbados Light & Power owned transformer and associated switchgear. The customer is provided with a low tension supply and is metered on the secondary or low tension side of the transformer and is billed at the Secondary Voltage Power (SVP) tariff. The company retains responsibility for the maintenance of the equipment. The basic voltages available to Secondary Voltage Power (SVP) customers are as follows:
• 115/200 Volts, 3 phase, 4 wire
• 115/230 Volts, 3 phase, 4 wire (see Note 1.)
• 230/400 Volts, 3 phase, 4 wire (see Note 2.)
For installations greater than 200 amps (75 kVA) the Company will normally require either a well ventilated, lockable room provided by the customer to house the Company's transformers or a concrete pad for the installation of a Company owned padmount transformer. With these installations the secondary terminals of the transformer constitute the point of entrance.
1. 115/230 Volt, Three Phase - In cases where a 115/230 volt three phase supply is required by the customer, the Company will normally install two (2) single phase transformers in an Open Delta configuration. The open delta connection is only provided in circumstances where the transformers are installed on the customer's property and away from the main overhead supply. 115/230 three phase is not available using a single three phase padmount transformer.
2. In cases where a 230/400 volt three phase supply is required by the customer, the Company can install either three (3) single phase transformers or a padmount transformer. This service is only provided in circumstances where the transformers are installed on the customer's property and away from the main overhead supply.
Three options are available to customers who require three phase electricity supply using transformers supplied by The Barbados Light and Power Company Limited.
• Polemount transformers.
• Vault transformers in a Transformer Room.
• Padmount transformers.
The type of transformer installation will depend on the type of supply that is required by the customer (size and voltage) as well as other factors such as the location (e.g. Bridgetown, industrial estate).
Three phase supply up to 200 amps can be provided from a pole. For services greater than 200 amps the customer must make provision for the installation of a padmount transformer or provide a transformer room for the installation of vault type transformers.
The voltages available for three phase overhead supplies are as follows:
• 115/200 Volts, 3 phase, 4 wire
• 115/230 Volts, 3 phase, 4 wire (see Note 1. on preceding page)
• 230/400 Volts, 3 phase, 4 wire (see Note 2. on preceding page)
Note: In most areas of Bridgetown it is not possible to install polemount transformers. For services up to 200 amps capacity, the customer must provide space for a service pillar / turret where underground three phase distribution is available. For loads greater than 200 amps or where underground three phase distribution is not available, the customer must provide a Transformer Room.
Padmount Transformer Installations
Three phase padmount transformers available in the following sizes.
• 112.5, 150, 225, 300, 500, and 750 kVA.
The following voltages can be supplied from a three phase padmount transformer.
• 115/200 Volts, 3 phase, 4 wire
• 230/400 Volts, 3 phase, 4 wire
Padmount transformers offer several advantages to the customer. Some of these advantages are listed below.
1. Padmount transformers can be installed outdoors on a simple concrete pad. This eliminates the need for the customer to provide a Transformer Room resulting in considerable savings.
2. Padmount transformers need less space than Transformer Rooms.
3. From a safety point of view the padmount transformers are designed to be tamper proof and weatherproof. Padmount transformers are designed to be either Radial or Loop Feed.
Radial Feed transformers are used where only one transformer is being fed via the underground high voltage cable.
Three conduits are installed for the cables which feed the transformer.
Loop Feed transformers are used where several transformers are to be fed in series from the high voltage cable. The transformer contains two sets of connections each consisting of three bushing wells. The three incoming high voltage cables which feed the transformer are connected to one set of bushing wells while the outgoing cables which continue on to feed the next transformer are connected to the second set of bushing wells. A total of six conduits is required - three for the incoming cables and three for the outgoing cables.
Typical three phase padmount transformer installations are shown in Figure 13 Installation Details
• Concrete Pad - The concrete pad size has been standardised to allow a transformer to be replaced in the future with one of a different size or make. This may become necessary due either to an increase in the customer's demand or because maintenance needs to be carried out on the existing transformer. Figures 14A and 14B show the standard arrangement for the concrete pad.
• HT ducts - For Radial Feed transformers, three (3) 100 mm internal diameter (4 inch) ducts are required for the high voltage cables from the cable drop at the pole to the transformer pad. Three (3) single core 1/0 XLPE cables will be used to supply the transformers.
For Loop Feed transformers, six (6) 100 mm ducts are required, three (3) ducts for the incoming high voltage cables and three (3) ducts for the outgoing cables from the transformer to another padmount transformer location. For safety reasons the Company requires that the conduits for the cables be buried at a minimum depth of 750mm (2' 6") and be separated by at least 300 mm (1 foot) from underground facilities belonging to other utilities. Where the required depth cannot be achieved appropriate mechanical protection (e.g. concrete) can be used provided that prior approval has been obtained from the Company.
• Access - In order to carry out maintenance and other checks it will be necessary for the transformer to be located so that it will be accessible to the Company's personnel at all times. Clear vehicle access should be maintained right up to the transformer.
• Physical Protection - In instances where the padmount will be placed near to an area which has vehicular traffic it will be necessary to provide removable barriers to prevent accidental damage.
• Meter Location - Where a single customer is fed from a padmount transformer it is possible to install metering Current Transformers (CTs) on the secondary bushings of the padmount transformer. These CTs will be provided by the Company. The meter can be located on the side of the padmount transformer or on a suitable concrete pillar adjacent to the transformer in a location easily accessible by the Company's meter reader. (see Figure 16) .
In cases where several customers are supplied from a padmount transformer the requirements for meter/multi-metering as specified in this booklet should be adhered to.
High Tension (HT) primary service is available at either 11,000 or 24,900 Volts, depending on location. It is important that the customer consult the Company in advance of making plans for the use of high tension service.
Transformer and High Voltage Switchgear
For primary supply, the customer must purchase and install a suitable transformer to change from the primary to the secondary voltage. The secondary voltage is the customer's choice. Details on the primary voltage and recommended voltage taps will be provided to each customer by the Company. The customer must install such high voltage switchgear as the Company and GEED may require. High voltage switchgear should have a short circuit interrupting capacity of 250 MVA. The complete installation must conform to the requirements of the Company and the GEED. In areas of Bridgetown where the high tension supply is underground, additional space will be required to accommodate a High Tension Metering Unit.
Transformers and switchgear located outdoors must be designed and installed so that they are protected from mechanical damage and all live parts are inaccessible to unauthorized personnel.
The Company is prepared to supply and install an underground high voltage service cable at the customer's expense. The cable route will be decided by the Company in consultation with the customer. The customer will be required to install fibreglass or PVC ducts to contain the high voltage cables. The sizes, and radius of bends will be specified by the Company. The radius of bends is normally one metre.