SANKEN ELECTRIC : Inverter

SAMCO-e Series

Noises

Inverter noise

This noise is generated due to switching in the inverter block. Noise current (i) is released to the ground through the stray capacitance (C) that exists between the inverter, cable and motor and the ground at each switching. The noise current at this time, which is represented by the following equation, affects the stray capacitance (C), dv/dt (switching speed) and switching frequency.

i=C*dv/dt

Although the above noise frequency band affects the reception of AM radio, which uses a low frequency band under approximately 30 to 40 MHz, FM radio and television, which use a higher frequency band, are hardly influenced.

Types of noise

Conduction noise
This is noise generated inside the inverter, and which travels through conductors and influences peripheral devices. (This noise travels through the input power supply. If the grounding wire uses a common connection, the noise travels through the signal line or shielded wire of a sensor or other part.)
Inductance noise
This is noise induced by electromagnetic induction and electrostatic induction to the wires of peripheral devices and signal wires when the signal wires (small signal wires) of peripheral devices are placed near the input/output wiring (power wire) of an inverter in which noise current flows.
Emission noise
This type of noise occurs when the noise generated inside the inverter is radiated into the atmosphere by the input/output wiring, which acts as an antenna, affecting peripheral devices.

When housing the inverter into the control panel, take the following points into consideration during installation.

Precautions

Separate power-system-related wires and signal-system-related wires. Try to avoid influence from the control signal wires.
Use a shielded wire, twisted shielded wire, metal pipe or other appropriate wiring for the signal system.
(Connect the shield to the common side of signal line (one point connection). Do not adopt multipoint connection, to avoid loop formation.)
Reduce the noise level, lower the emission level and prevent noise propagation.
Perform the most appropriate grounding. Be sure to connect the shield of a shielded wire to a single point. (Connect it to the common side of a signal line, avoiding multipoint looping.)
Install the noise filter (e.g., zero-phase reactor, radio noise filter, I/O noise filter).
Use a power supply transformer.

It is also effective to install the shield, line filter, choke coil, ferrite core bead, and installation line, and take other measures at the noise receiving side.

Noise Suppression Examples

Noise suppression list

Phenomenon	(Possible) Cause	Precaution	Remark
1. Noises affecting AM radios	Emission noise from the power supply side Emission noise from the output side Emission noise from the power line at the power supply side Radiation noise for which the grounding line acts as antenna	Install an LC filter at the power supply side. Use a metal pipe for wiring at the inverter output side. Adopt shielded wiring. Reduce the carrier frequency. Install an inductive filter at the input/output sides or output side. Roll the coil of a zero-phase reactor as many times as possible. Install an LC filter (input/output). 3'S.ª,ð Notes on grounding wire Keep an appropriate distance between the grounding wire and the peripheral devices. House the grounding wire into a metal pipe. Use a 4-core cable and use one of its wires for grounding.	Emission noise Radiation noise
2. Telephone noise	High-frequency current leakage from the inverter and motor (Current leaks to the shielded grounding section of the telephone cable via the grounding wire, generating noise due to electrostatic induction.)	Adopt a common connection with the grounding terminal of motor, return it to the inverter panel and install the capacitor between the input terminal and grounding terminal.	Inductance noise
3. Malfunction of pressure sensor	Noise has traveled through the shielded wire and entered into the pressure sensor.	Install the LC filter at the input/output side. Change the shielded wire for the pressure sensor from the device case to the 0 V line of the pressure sensor (common).	Conduction noise
4. Malfunction of programmable controller	Noise has traveled through the power supply and entered into the programmable controller.	Install the capacitive filter and LC filter at the input side. Install the LC filter at the output side. Reduce the carrier frequency.	Conduction noise
5. Malfunction of encoder	Inductance noise from the power line or signal line	Install a capacitive filter and an LC filter at the input side. Install an LC filter at the output side.	Inductance noise Emission noise
6. Malfunction of peripheral device	Noise has traveled through the inverter and the stray capacitance between the input/output wire and equipment wire and entered into the device. Inverter noise has entered into the device through the wire at the power supply side. The magnetic field for the inverter input/output current opened and interlinked with the device wire, resulting in noise induction.	Use a shielded wire with two or more cores for the signal line. Separate the power supply system. Install a noise filter at the power supply side. Install a noise cut transformer. Use a 3-core cable for input/output wiring. Keep a distance between the main circuit wire and device signal line.	Conduction noise Inductance noise
7. Malfunction of inverter	Malfunction of relay or electromagnetic contractor Malfunction of control signal Inappropriate grounding method	Install a surge killer in the coil section. Use a shielded wire or twisted pair line. Dedicated grounding is the most desirable. The grounding point should be as close as possible. The grounding wire must be short and separated from other power lines and signal lines.

Noise Suppression List

When the inverter causes noise

1	Noise propagated through the wiring at the power supply side
	Install the noise filter at the power supply side.
	Install the noise filter at the power supply side of corresponding device.
	Install the noise cut transformer (Be sure to ground the shield.)
	Ensure that the power supply is separated.
2	Radio noise (noise propagated through air)
	Install an input noise filter at the power supply side.
	Put the output-side wire into a metal pipe (to remove radiation and inductance noises).
	Wrap the output-side wire, grounding wire or other wire with a tube or other material.
	Keep a distance between the wires and the affected device (at least 10 m).
	Shield the wires of the affected device.
	Shield the inverter itself, covering it with a metal case.
3	Inductance noise (electromagnetic induction or electrostatic induction).
	Use a shielded wire or a twist wire as a control signal line (Ground the shield at a single point).
	Separate the power line and control line.
	Shield the power line and control line.
	Wire another route and check the inductance influence.

When the inverter is affected

1	The inverter malfunctions and stops working.
	Check that there are no devices generating surge or noise.
	Install a surge killer onto the coil of an electromagnetic switch, relay, or other part.
	Ensure that a shielded wire or twist wire is used as a control signal line.
	Ensure that grounding is appropriate.
	Ensure that one-point dedicated grounding has been performed.
	Ensure that C- or D-type grounding has been performed.
	Ensure that the grounding wire is sufficiently thick and as short as possible.
2	The operation of inverter is unstable.
	Ensure that the shielded wire or twisted wire is used as the control signal line.
	Separate the power line and control line.
	Wire another route and check the inductance influence.

Generally, the inverter noise affects the corresponding device depending on the conditions below.

Noise capacity and sensitivity of corresponding device and communication device
In the case of a communication device, the influence level varies depending on the electric field intensity of the received radio wave.

Install a noise filter if the electric field intensity is weak, because the device is affected by the inverter.