Types Of Submeters
Cashpower Power Rail Wired
Rail-mounted split prepayment meter
The Cashpower Power-Rail is a single-phase 60A (80A optional) split meter in a DIN rail-mount housing. Ideal for new reticulation where housing is informal and the prepayment meters are mounted in a pole-top enclosure with respective customer interface units conveniently mounted in the dwellings below. Due to the small size and DIN rail housing, multiple Power-Rail meters can be mounted in a small enclosure thereby making installation cost-effective.
Split meter concept
The Cashpower Power-Rail consists of two parts: the Customer Interface Unit and the Meter.
The Customer Interface Unit is a compact unit with a user-friendly display and keypad that can be installed in any convenient location inside the consumer’s premises. Connection to the remotely installed meter is via a pair of communications wires. The connection of these wires at the meter is achieved by means of a plug-in connector, facilitating easy installation and maintenance.
The meter contains all critical metering, number decryption and load control functionality. It operates independently of the customer interface unit and is immune to any form of tampering on the customer interface.
The meter is usually installed in a secure, locked enclosure - typically a pavement kiosk or pole-mounted equivalent. It is outside the consumer’s premises to facilitate easy inspection by the utility at any time, thus reducing the possibility of tampering.
Principle of operation
The Cashpower Power-Rail meter in the Energy Limiting Mode provides utilities with the utmost flexibility in terms of being able to adapt to a range of different consumer profiles. Three utility-programmable modes of operation are available and it is possible to switch between modes as required:
Energy Limiting Mode
This mode allows utilities to distribute a fixed, monthly allocation of energy to consumers. It encourages the rational use of energy without severely inconveniencing the consumer. Operation is as follows:
Assume that a monthly energy allowance of 150kWh has been allocated to a consumer. The meter allocates this energy in regular, equal portions over the thirty-day period i.e. by incrementing the kWh credit level with a value of 0.00087kWh every 15 seconds.
Assuming that the consumer draws no power at all, the credit level will continue to increase. However, as soon as energy starts to be used the credit level is proportionately decremented. If the rate at which energy is being used is less than the rate at which it is being incremented, the credit level will slowly continue to increase. If the rate at which energy is being used is greater than the rate at which it is being incremented, the credit level will slowly decrease. It is in the consumer’s interest to ensure that electricity is not wasted and that unnecessary appliances are turned off. By conserving energy, it will be possible to use it at a high rate for periods when required.
In the event of the consumer exceeding the allocated allowance (credit level reduced to zero), the load is disconnected. However, the next allocation of credit will be available within a very short period of time (15 seconds) and the supply of electricity restored. Providing the consumer takes immediate steps to disconnect unnecessary appliances, it will be possible to have at least basic services available e.g. lighting. With a 150kWh monthly allocation of energy, it will be possible to maintain a continuous load of 200W whilst still maintaining a positive credit balance.
Prepayment mode
In Prepayment metering mode it functions as a normal prepayment meter. Credit tokens are purchased and entered into the meter via the customer interface unit keypad. On expiry of credit the load is disconnected and will only be re-connected when a valid credit token, purchased by the consumer, is entered.
Credit mode
In Credit metering mode it functions as a conventional credit meter. Power is continuously supplied to the consumer and total kWh’s used is continuously measured and recorded. The meter must be read by the utility at regular intervals and the consumer billed accordingly.
Automatic / manual supply re-connection
A programmable function allows for either automatic or manual restoration of power to the load after it has been disconnected for a period due to expiry of credit or Power Limiting. Manual restoration is accomplished via the customer interface unit.
User-friendly customer interface
The meter is controlled via the customer interface unit in exactly the same way as other meters in the Cashpower meter range. User interaction with the meter and access to meter information e.g. rate of energy consumption, low credit warning and load contactor status, is available using the customer Interface’s keypad and large LCD. The customer interface unit makes use of clear, language-independent icons. The user interface is further enhanced by the use of audible tones. These are sounded under different conditions e.g. Low Credit Alarm and Token Accept.
Meter status and diagnostic indicators
The meter includes an LED status indicator. This allows a technician to view the state of the meter without the need for specialised interrogation tools or having to gain access to the consumer’s premises. Information such as Tamper status, Power Limiting, Commissioned/Decommissioned status and Remaining Credit status are available.
The meter also features a dedicated diagnostic LED for the Customer Interface. It can indicate the presence of “Open” or “Short” circuited communication lines. This is a valuable visual aid that assists the technician to validate the installation and determine probable fault types.
Interrogation port
As a customer option, more detailed information and programming is achieved via the standard interrogation port on the side of the meter.
Optical interface
As a standard feature, the meter has an IEC 62056-21 compliant optical communications port. This allows the utility to access a variety of information stored inside the meter and to upload it to a hand-held unit.
Tamper detection
The split configuration of the meter significantly reduces the risk of tampering. The meter is installed in a remote, secure location and is mechanically sealed against tampering through the use mechanical clips and inaccessible assembly screws. Utility-sealed wire seals can be field-fitted to secure the main power cable terminations. The use of these mechanical seals ensures that there will be visible signs of tampering if unauthorised entry to the system is attempted.
The meter also has a feature allowing detection of Significant Reverse Energy (SRE). If the line and load wires are swapped during installation, the meter will continue to operate and decrement credit. The unit may be factory programmed to Tamper and disconnect the consumer’s load should SRE be detected.
Disconnect on Power Fail
The meter includes a feature to cater for a condition where the neutral link to the device is removed. The meter can be personalised to disconnect the load if a power failure is detected, as would be the case if the neutral wire were to be removed.
Surge protection
The meter has been designed to have a surge voltage withstand that significantly exceeds the requirements of both SABS 1524 and IEC 62052-11. Depending on the installation’s electrical environment, the customer has the option to fit an additional surge arrestor with a current surge rating in excess of 30kA.
Installation features
The meter is suited for connection to most metering and reticulation systems. The communication wires for the customer interface are non-polarised and safety-isolated. This simplifies the installation process and also ensures safety within the consumer’s premises. The communication wires can be included as separate cores in a concentric reticulation cable and provide a very robust communications interface between the meter and the customer interface over a distance of at least 130 metres.
