Diagnosis through electrical measurement

Electrical measurements

Voltage and current, two key values for understanding (almost) everything

As far as electrical measurements are concerned, voltage and current are the two values on which other values are based (power, energy, power factor, etc.).
You should have a full range of measuring devices capable of providing the specific measurements required for the application. You can significantly increase the value of your information by obtaining other data from the same measurements:

• Operating positions for devices (start/stop, open/closed, etc.)
• Number of operating hours/switching operations
• Motor load
• Battery charge
• Equipment failures
• etc.

There is no such thing as a “one-size-fits-all” solution. It is a question of finding the best compromise, in technological and financial terms, for the particular needs of the given situation, whilst remembering that measurement accuracy involves costs which have to be compared against the anticipated returns on investment.
In addition, when the operator’s electrical network is expected to undergo frequent changes given the activities in which it is involved, these changes should prompt a search for immediate and significant optimisation measures.
Approaches to energy efficiency also need to take other parameters into account (temperature, light, pressure, etc.), since, assuming energy is transformed without any losses, the energy consumed by a piece of equipment may exceed the useful energy it produces. One example of this is a motor, which converts the energy it consumes into heat as well as mechanical energy.

Collating relevant electrical data for specific objectives

As well as contributing towards energy efficiency, the information gleaned from electrical data is commonly used to support a number of other objectives:

• Increasing user understanding and providing opportunities for optimising equipment and procedures
• Optimising functionality and extending the service life of equipment associated with the electrical network
• Playing a pivotal role in increasing the productivity of associated processes (industrial or even administrative/management procedures) by avoiding/reducing periods of lost productivity and guaranteeing the availability of a high-quality energy supply

Adapted measuring instruments

Electronic equipment is increasingly replacing analogue equipment in electrical installations. It supports more accurate measurement of new values and is able to make these available to users at both local and remote locations.
All these various measuring devices (referred to as “PMD” for “Performance Measuring and Monitoring Device”) have to meet the requirements of international standard IEC 61557-12. According to this standard, devices have a code denoting their installation options, operating temperature range and accuracy class. As a result, it has become significantly easier to select and identify these devices (see Fig. K4).

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Fig. K4: Identifying measuring devices in accordance with IEC 61557-12

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A number of devices have been designed for inclusion in this category. These include Sepam overload and measuring relays, TeSys U motor controllers, NRC 12 capacitor battery controllers and Galaxy outage-free supply devices. The new Masterpact and Compact circuit breakers with integrated Micrologic measuring devices (seeFig. K5) also simplify matters by multiplying measurement points.

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Fig. K5: Compact NSX circuit breaker equipped with a Micrologic trip unit and TeSys U controller (Schneider Electric)

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It is also now possible to broadcast measurements via digital networks. The table in Figure K6 shows examples of measurements available via Modbus, RS485 or Ethernet.

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	Units of measurement	MV measurement and overload relays	LV measurement and overload relays	Capacitor battery controllers	Monitoring and insulation devices
Examples	Circuit monitoring device, kilowatt hour meter	Sepam	Masterpact and Compact Micrologic circuit breakers	Varlogic	Vigilohm system
Control of energy consumption
Energy, inst., max.,   min.	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	-
Energy, reclosing capability	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	-	-
Power factor, inst.	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	-	-
Cos φ inst.	-	-	-	[math]\displaystyle{ \blacksquare }[/math]	-
Improved energy availability
Current, inst., max., min., imbalance	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	-
Current, wave form capture	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	-	-
Voltage, inst., max., min., imbalance	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	-
Voltage, wave form capture	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	-	-
Device status	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	-
Fault history	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	-	-
Frequency, inst., max., min.	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	-	-
THDu, THDi	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	-
Improved electrical installation management
Load temperature, thermal state of load and device	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	-	[math]\displaystyle{ \blacksquare }[/math]	-
Insulation resistance	-	-	-	-	[math]\displaystyle{ \blacksquare }[/math]
	Motor controllers	LV variable speed drives	LV soft starters	MV soft starters	Outage-free supply devices
Examples	TeSys U	ATV.1	ATS.8	Motorpact RVSS	Galaxy
Control of energy consumption
Energy, inst., max., min.	-	[math]\displaystyle{ \blacksquare }[/math]	-	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]
Energy, reclosing capability	-	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	-
Power factor, inst.	-	-	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]
Improved energy availability
Current, inst., max., min., imbalance	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]
Current, wave form capture	-	-	-	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]
Device status	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]
Fault history	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	-
vTHDu, THDi	-	[math]\displaystyle{ \blacksquare }[/math]	-	-	-
Improved electrical installation management
Load temperature, thermal state of load and device	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]
Motor running hours	-	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	[math]\displaystyle{ \blacksquare }[/math]	-
Battery follow up	-	-	-	-	[math]\displaystyle{ \blacksquare }[/math]

Fig. K6: Examples of measurements available via Modbus, RS485 or Ethernet