Diagnosis through electrical measurement

Electrical measurements

The first step in an Energy Efficiency approach is to establish a diagnosis and primarily aims to get a better idea of where and how energy is being consumed. This requires the development of initial measures and a comparative assessment process with a view to evaluating performance, defining the main areas for improvement and estimating achievable energy saving levels. The logic behind this approach is based on the realization that "you can only improve what you can measure".

With a large scope and detailed list of requirements, IEC 61557-12 is applicable to measuring devices addressing most applications in switchboards and panels worldwide.

Stand-alone Power Measurement Devices are the natural solution of obtaining relevant data at the most important points in the electrical installation. A large range of devices is available from manufacturers, covering the full range of voltage and current, providing data about a large number of different electrical quantities (voltage, current, power, energy, etc.), with local display or remote communication capabilities.

However, many advantages can be gained by combining the functions of measurement and protection in one single device.

Firstly, this approach leads to a reduction in equipment installation costs: installing one single device costs less than installing two.

And combining these two functions in the same unit ensures the right sizing of current sensors, and eliminates risks of connection errors and guarantees correct operation, with the whole unit tested in the factory.

Examples of architectures including both types of devices are presented in Energy saving opportunities - Smart Panels.

How to select relevant measuring instruments

French standard AFNOR “FD X30-147 Measurement plan – design and implementation” published in November 2015 and described hereafter is currently the most advanced document about concrete ways to build a measurement plan.

This document proposes 3 levels of achievement :

• Base level
• Medium level
• Advanced level

Tables in Annex F of this standard define the appropriate measurements required to achieve each level of achievement of the measurement system. Some extracts are shown in following paragraphs.

Measurement by zone or by mesh

Measurement of active energy need to be achieved zone by zone, or mesh by mesh:

Fig. K11 – Appropriate measurements for electrical energy

Measurement to be done	Relevant measurements
	Base	Medium (in addition to base)	Advanced (in addition to medium)
For each zone or mesh	Active energy	Reactive energy Apparent energy Power	---

Measurement by usage

Attention should be put on measurement by usage that can be helpful to determine potential sources of energy efficiency improvements:

Fig. K12 – Appropriate measurements according to the uses

Measurement to be done	Relevant measurements
	Base	Medium (in addition to base)	Advanced (in addition to medium)
HVAC	Active energy	Internal temperature Hygrometry Coefficient of Performance (COP)	---
Lighting	Active energy	---	---
Appliances	Active energy	---	---
Motors	Active energy	Reactive energy	THDi Unb (Unbalance)

Measurement of relevant variables

ISO 50006 is providing guidance on "energy base line” and on “Energy Performance Indicators”. These items are mixing energy measurement with other relevant parameters, e.g. measurement of energy consumption correlated with degree-day, or energy consumption related to the number of persons present within a plant, or other influencing parameters.

All these relevant parameters need to be measured or estimated or transferred from another database.

Fig. K13 – Appropriate measurements of influencing factors according to uses

Measurement to be done	Relevant variables
	Base	Medium (in addition to base)	Advanced (in addition to medium)
HVAC	Outside temperature (or degree day)	Inside temperatures Inside hygrometry Number of persons present or equivalent indicator (e.g. daily turnover)	HVAC Coefficient of Performance (COP) HVAC power
Lighting	Season	Natural lighting Number of persons present or equivalent indicator (e.g. daily turnover)	---
Appliances	---	Number of persons present or equivalent indicator (e.g. daily turnover)	---
Motors	---	Surrounding temperature	---
Generators	---	Surrounding temperature	---

Monitoring of electrical installation

It is also important to monitor the electrical distribution system, because some measurements can reveal some issues with energy efficiency, and additionally some risks related to assets.

Fig. K14 – Appropriate measurements according to the type of outgoing line, incoming line, generator or energy exchanger

Measurement to be done		Relevant variables
		Base	Medium (in addition to base)	Advanced (in addition to medium)
Delivery point	At delivery point	Active energy	Voltage, Current, Power Factor, active/reactive energy and power,THDu and THDi, frequency	Individual harmonics voltage and current
Distribution Switchboard	for each feeder with at least 100kVA power (e.g. : 160A, 400V tri)	Active energy	Voltage, Current, Power Factor, active/reactive energy and power, THDu and THDi, frequency	Individual harmonics voltage and current
	for each feeder with at least 40kVA power (e.g. : 63A, 400V tri)	---	Voltage, Current, Power Factor, active/reactive energy and power	THDu and THDi
	for each feeder with at least 3.5kVA power (e.g. : 16A, 230V single phase)	---	---	Active energy
Transformers	Transformers	---	Transformer efficiency	Voltage unbalance, upstream and downstream voltage