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Diagnosis through electrical measurement

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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:

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

---

Fig. K11Appropriate measurements for electrical energy

Measurement by usage

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

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)

Fig. K12Appropriate measurements according to the uses

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.

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 ---

Fig. K13Appropriate measurements of influencing factors according to uses

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.

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

Fig. K14Appropriate measurements according to the type of outgoing line, incoming line, generator or energy exchanger