General Description
1. Current transformer, also referred to as instrument transformer, is used to convert high AC current to small, easily manageable value.
2. Current transformer is mainly composed of primary winding, secondary winding, magnetic core and insulated body. It is manufactured without primary winding if it has no bus bar. Instead, it is possible to constitute primary winding by passing conductor or bus bar inside toroidal core of transformer.
3. Furthermore, the secondary terminals are under a transparent cover. Low voltage current transformer is manufactured as of two types for measuring and protection.
Measuring Current Transformer
1. It is manufactured to feed on other low voltage apparatus such as measuring instrument, relay, watt-hour meter.(kW meter).
2. This type of current transformer is mainly used 0.5 and 1 class to transfer the current from high rated current to rated secondary current.
Protection current transformers
1. It is constructed to feed the protection relay.
2. This type of current transformer is mainly used class 3.0(Customer supplied when required)
Technical Characteristics
| Maximum rated voltage | 720V |
| Typical application | Indoor |
| Continuous operating current | 1,2xIn |
| Test voltage per minute | 4kV |
| Security coefficient | 5 |
| Rated primary current(In) | 30A-6000A |
| Rated secondary current | 5A |
| Operating frequency | 50-60Hz |
| Operating temperature | -5°C/+45°C |
| Thermal rated current | 1th=100xIh(for MSQ-A type Ith=60xIn) |
| Dynamic rated current | Idyn=2.5xIn |
Notes:
1. Ratio error of current transformer can be guaranteed between 100% and 120% of rated current.
2. Error class can be 2-3 folding, especially the value of the under half rated current at the application, load current can be taken into consideration between In-1.2In.
Current Errors and Phase Shift In Measuring Current Transformer
| Accuracy Class | Permissble error±at Various percentage of rated Secondary current (±) | ±phase shift in various percentages of rated secondary current | ||||||||||
| Minute (±) | Centiradian (±) | |||||||||||
| %5 | %20 | %100 | %120 | %5 | %20 | %100 | %120 | %5 | %20 | %100 | %120 | |
| 0,2 | 0.75 | 0.35 | 0.2 | 0.2 | 30 | 15 | 10 | 10 | 0.9 | 0.45 | 0.3 | 0.3 |
| 0.5 | 1.5 | 1.5 | 0.5 | 0.5 | 90 | 45 | 30 | 30 | 2.7 | 1.35 | 0.9 | 0.9 |
| 1.0 | 3.0 | 3.0 | 1.0 | 1.0 | 180 | 90 | 60 | 60 | 5.4 | 2.7 | 1.8 | 1.8 |
Current Errors and Phase Shift In Protection Current Transformer: [Fault Conditions]
| Accuracy Class | Permissible error±at Various percentage of rated secondary current | ±Phase shift in various percentages of rated secondary current | Compound error for rated current% | |
| Minute | Centiradian | |||
| 5P | ±1 | ±60 | ±18 | 5 |
| 10P | ±3 | -- | -- | 10 |
Device Power Which Connected to Current Transformers
| Devices | Power(VA) |
| Ammeter | 0.7 --- 1.5 |
| Wattmeter | 0.2 --- 5.0 |
| Wattmeter | 2.0 --- 6.0 |
| KWh-meter(active and reactive) | 0.4 --- 1 |
| Reacive power control units | 12 |
| Overload relays | 0.2 --- 6 |
| Inverse current relays | 2 |
| Secondary thermal relays | 7.2 --- 9 |
English
Español