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

European standard EN 17267 "Energy measurement and monitoring plan for organisations - design and implementation - Principles for energy data collection" published in 2019 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 B 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 (EN 17267, Table B1, extracts)
Criterion 1: Ability to quantify the energy consumption by zone and by energy use Base Medium High
Monitoring of consumption per zone
Each site (connected to the utility grid through a billing meter) is considered as a zone X X X
Each facility (within a site) is considered as a zone X X
Each facility is divided in zones (workshop, office, floors, …) X
Monitoring of consumption per energy use
The appropriate consumption measurements per monitored energy are performed (see Table B.2) X X X
At least one significant energy use is identified and monitored per zone (see Table B.3 and Table B.4) X X X
Several significant energy uses are identified and monitored per zone (see Table B.3 and Table B.4) X X

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 per use (EN 17267, Table B4)
Energy use Types of measurements
Base Medium (in addition to base) High (in addition to medium)
HVAC (heating, ventilation and air conditioning) Active energy Internal temperature
Hygrometry
COP (Coefficient Of Performance)
--
Lighting Active energy –- –-
Electrical devices (PCs, printers, etc.) Active energy –- –-
Motors Active energy Reactive energy THDi
Unb (voltage unbalance)
Generators Active energy produced –- Efficiency (if calculable)
Compressed air pump Active energy Reactive energy
Standardized air flow rate
Pressure
Specific consumption
Hot water and steam production system Energy consumption Thermal power produced Efficiency
Refrigeration system Active energy Reactive energy
Refrigeration power produced
Efficiency
COP (Coefficient Of Performance)
  • NOTE: Some of these quantities are calculated from raw measurement data (Efficiency, COP).

Measurement of relevant influencing factors

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 factors.

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

Fig. K13 – Appropriate measurements of influencing factors per use (EN 17267, Table B5)
Energy use Types of measurements
Base Medium (in addition to base) High (in addition to medium)
HVAC (heating, ventilation and air conditioning) Outside temperature or degree day Occupancy rate Power of the HVAC
Lighting Season Natural light
Occupancy rate
–-
Electrical devices (PCs, printers, etc.) -- Occupancy rate –-
Motors -- Temperature in vicinity –-
Generators -- Temperature in vicinity –-
Compressed air pump -- Temperature in vicinity –-
Hot water and steam production system -- Water temperature at inlet
Temperature in vicinity
–-
Refrigeration system -- Temperature in vicinity --
  • NOTE: The influencing factors are chosen according to the sector of activity.

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 (EN 17267, Table B7)
Equipment topological position Types of measurements[a]
Base Medium (in addition to base) High (in addition to medium)
Point of delivery At point of delivery Active energy U (voltage) and I (current)
f (frequency)
Power Factor (or cos phi)
Reactive energy
Active/reactive power
THDu and THDi (total harmonic distortion)
Individual current and voltage harmonics
Distribution Switchboards For each outgoing line of at least 100kVA[b] power (e.g.: 160A, 400V 3-phase) Active energy U (voltage) and I (current)
Power Factor (or cos phi)
Reactive energy
Active/reactive power
THDu and THDi (total harmonic distortion)
Individual current and voltage harmonics
For each outgoing line of at least 40kVA[b] power (e.g.: 63A, 400V 3-phase) Active energy U (voltage) and I (current)
Active/reactive power
Power Factor (or cos phi)
THDu and THDi (total harmonic distortion)
Load For each outgoing line of at least 3.5kVA[b][c] power (e.g.: 16A, 230V single-phase) -- -- Active energy
Transformer Electrical transformers -- Efficiency Unb (voltage unbalance)
U (upstream and downstream voltage)
  1. ^ Depending on the application and the objectives, other measurements can be put in place (example: unbalance, alarm when threshold is exceeded, etc.).
  2. ^ 1 2 3 The power depends on the type of installation and the buildings: tertiary, commercial, industrial, infrastructure, etc.
  3. ^ Buildings such as datacentres necessitate monitoring of the loads of more than 2,3 kVA (e.g. 10A, 230V).
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