Definition – HT panel is a metal enclosure fitted with HT Circuit Breakers, relays &metering that is used to receive 11KV/33KV supply (from one or more source) & distribute the power through its outgoing feeders. Outgoing feeder may be one or more it depends on the load of the building.
HT panel is installedin substations of Commercial complexes, residential colonies, factories, schools, hospitals etc. to receive & distribute HT supply.
Main functions of HT panel –
- To make & break HT supply (or switch on or switch off supply),
- To receive & distribute HT supply,
- To provide protection against faults,
- To provide metering to monitor various parameters.
Features of HT panel (for 11KV or 33KV) –
- HT panel receives electrical Supply 11KV or 33KV) from H – poleby 3 core HT cable & then it distributes power through one or more outgoing feeders.
- These outgoing feeders are connected with distribution transformers which convert HT supply into 415V, 3-phase 4 wire AC supply.
- To measure electrical power consumption, Energy Meter is installed in it,
- Meters are installed to measure electrical Voltage, Current, frequency, power factor etc.
- Transformer protection relays are installed in it such as –
For Dry type transformer – WTI (Winding Temperature Indicator) – Alarm & Trip,
For Oil type Transformers – WTI & OTI (Oil Temperature Indicator) – Alarm & Trip and Buchholz relay (gas operated relay) – Alarm & Trip.
- Short circuit protection, over load protection, earth fault protection relays can be installed in it against protection from faults.
- HT Circuit Breakerssuch as VCB, SF6, etc but VCB is the most commonly used HT breaker are used to make & break HT supply.
- HT circuit breakers can be switched ON & OFF either manually or electrically.
- 24V (or 30V) DC supply which is an external source to HT panel is used for various purposes like for metering, relay operations, indicating lights,
- 240 V ac supply is also used in HT panel for 16A power sockets provided inside panel, for panel lights & space heater.
- Space heater is provided in HT panel to avoid moisture inside the panel.
- To measure Incoming Supply voltage, 11KV is converted into 110V through PT (Potential Transformer). And 110V voltmeter is used for voltage measuring purpose.
- To measure building load in terms of current, total current of the building is converted into 5A or 1A through CT (Current Transformer). CTs are available in different range – 600/5A, 400/5A, 300/5A ….. or 600/1A, 400/1A, 300/1A …… A typical picture of HT panel is given below –