What is a Current Transformer (CT) and when to use it?

What is a Current Transformer (CT) and when to use it?

What's a Current Transformer? And when to use it?

Measuring the intensity of the electric current is a good method to control the electrical consumption of equipment, in a building, an industrial site, a use, a warehouse. The presence of current consumption, the level of current – in amperes – are indicators of activity.

The level of the current makes it possible, for example, to conclude on the level of operation of a machine (in standby, or the mode of operation – reduced, normal, intense). In a hotel, this makes it possible to deduce the presence of a person, or of an empty room whose electrical equipment is still active. In a building, this makes it possible to identify the level of (electrical) activity by zone.

If the placement of a communicating electricity meter allows, on the one hand to measure the current, but also to recover the power and especially the energy consumed, there are many cases where the budget and / or the complexity of installation of an electric meter is not justified.

The principle of a Current Transformer

An electric current creates a magnetic field. The current converter is a coil which is placed around a primary current phase. The magnetic field generated by the primary current will induce a much lower secondary current in the coil. This secondary current is proportional to the primary current. This principle therefore makes it possible to measure a current, even of high intensity, via an electronic device.

current-transformer-principle-magnetic-field-secondary-current

There are many models of Current Converters (CT), depending on the use required. The main characteristics of a current converter (CT) are:

  • Current rating: eg: 32A, 75A, 150A, 200A..
  • The conversion factor (therefore the secondary current): ex: 0.1A, 1A, 5A
    And the voltage level. For example: 5A; 0.333V
  • Shape and diameter. According to the dimensions of the primary phase
  • Measurement accuracy: 0.5%; 1%; 2%
  • The weight (from a few tens of grams)

Mistakes to avoid with CT

  • Electric current is measured on a single phase. The current converter must be placed on a current phase. An electrical device is always connected with at least 2 wires. You must place the converter on 1 phase (1 wire), not around the 2 wires.
  • Respect the maximum amperage authorized by the converter. Never exceed it. To do this, check the power of the machine, and the power of the circuit breakers in your electrical network. A 40A circuit breaker, for example, will not allow a current greater than 40A to pass.
  • Even if the placement of a converter is simple, it is recommended to hire a specialist (electrician) for the installation.

LORAWAN Current Transformer sensor

The LORAWAN current Transformer sensor is a simple to deploy, affordable device that allows the measurement of the current level, in amperes, at regular intervals.

The current measurement is carried out with a Current Converter (CT), which is placed around a current phase. It does not require any intervention on the network or the power supply. Due to the placement, the Current Trasnformers selected are of the “Split Core” type. This means that they can open (for placement around the cable – the phase) and then close again. You should therefore not interrupt the electrical equipment connected to the primary phase

Current measurement vs Electricity Meter

An electric meter measures the current, the voltage, the power, but also other parameters such as coefficient PF (Power factor), active, reactive and apparent power. The measurement is done continuously. Which is made possible, because it is mains powered

The LORAWAN current measurement sensor works differently. On the one hand it works on battery, which requires that it is not active continuously. On the other hand, it only measures the intensity of the current, and not the voltage. The operating principle is that it will measure the current at regular intervals. For example every 15 minutes. This means that possible highs/lows within 15 minutes are filtered out. Of course, if your current consumption is stable (for example a machine running – stable), the current measurement will give you a first estimate of the energy consumed (since in general, the voltage is constant – in reality, the voltage may vary by a few percent during the day).