# The Electrical Distribution Architecture – Part Four

In the previous Topic “The Electrical Distribution Architecture – Part Three“ , I list the Tasks required for application of Electrical Distribution architecture design process , they were:

• Assigning of electrical installation characteristics,
• Assigning of Technological characteristics,
• Using Architecture assessment criteria,
• Step (1): Choice of distribution architecture fundamentals,
• Step (2): choice of architecture details,
• Step (3): choice of equipment,
• Recommendations for architecture optimization.

And I began explaining the first task: Assigning of electrical installation characteristics which include the following categories or possible values:

1. Activity,
2. Site topology,
3. Layout latitude,
4. Service reliability,
5. Maintainability,
6. Installation flexibility,
7. Power demand,
9. Power Interruption Sensitivity,
10. Disturbance sensitivity,
11. Disturbance capability of circuits,
12. Other considerations or constraints

Today, I will continue explaining other tasks for helping you to use Electrical Distribution architecture design process professionally.

You can review the following previous topics for more information and good following:

 # Characteristic Definition Choice 8 Load Distribution A characteristic related to the uniformity of load distribution (in kVA / m²) over an area or throughout the building. Uniform distribution: the loads are generally of an average or low unit power and spread throughout the surface area or over a large area of the building (uniform density).E.g.: lighting, individual workstations Intermediate distribution: the loads are generally of medium power, placed in groups over the whole building surface area. E.g.: machines for assembly, conveying, workstations, modular logistics “sites” localized loads: the loads are generally high power and localized in several areas of the building (non-uniform density).E.g.: HVAC

The following table summarizes the effect of Load distribution Method on the Configuration of Electrical Distribution Architecture:

 Configuration of Electrical Distribution Architecture Loads Distribution Localized Loads Intermediate Distribution Uniform Distributed Layout#1 Layout#1 Layout#2 Layout#2

Layout#1 (see fig.1): The Electrical Distribution Architecture will be that each final load or final panelboards has its directly connected cable to the main low voltage switchgear.

Layout#2 (see fig.1): The Electrical Distribution Architecture will be that many loads or final panelboards will be connected to a busway or bus trunking system directly connected to the main low voltage switchgear.

 Fig (1): effect of Load distribution Method on the Configuration of Electrical Distribution Architecture

9- Power Interruption Sensitivity

 # Characteristic Definition Choice 9 Power Interruption Sensitivity The aptitude of a circuit to accept a power interruption. “Sheddable” circuit: possible to shut down at any time for an indefinite duration Long interruption acceptable: interruption time > 3 minutes * Short interruption acceptable: interruption time < 3 minutes * No interruption acceptable. * Indicative value, supplied by standard EN50160: “Characteristics of the voltage supplied by public distribution networks”.

We can distinguish various levels of severity of an electrical power interruption, according to the possible consequences:
1. No notable consequence,
2. Loss of production,
3. Deterioration of the production facilities or loss of sensitive data,
4. Causing mortal danger.

and This is expressed in terms of the criticality of supplying of loads or circuits as follows:

• Non-Critical: The load or the circuit can be “shed” at any time. E.g.: sanitary water heating circuit.
• Low Criticality: A power interruption causes temporary discomfort for the occupants of a building, without any financial consequences. Prolonging of the interruption beyond the critical time can cause a loss of production or lower productivity. E.g.: heating, ventilation and air conditioning circuits (HVAC).
• Medium Criticality: A power interruption causes a short break in process or service. Prolonging of the interruption beyond a critical time can cause a deterioration of the production facilities or a cost of starting for starting back up. E.g.: refrigerated units, lifts.
• High Criticality: Any power interruption causes mortal danger or unacceptable financial losses. E.g.: operating theatre, IT department, security department.

and The following table summarizes the suitable Power Interruption Sensitivity for different Configurations of Electrical Distribution Architecture (Supply side of Transformers) (see fig.2):

 Power Interruption Sensitivity Long interruption acceptable Short interruption acceptable Power Demand < 630KVA ≤ 1250KVA ≤ 2500KVA > 2500KVA > 2500KVA (And Several Buildings) Configuration Of Electrical Distribution Architecture (Supply side of Transformers) LV (No Transformers) MV Single-Line / Single Feeder Ring-Main Duplicate Supply / Open Ring 1 MV Substation Duplicate Supply With Double Busbars / Open Ring 2 MV Substations

 Fig (2):Configurations of Electrical Distribution Architecture (Supply side of Transformers)

and The following table summarizes the suitable Power Interruption Sensitivity for different Configurations of Electrical Distribution Architecture (Load side of Transformers) (see fig.3):

 Power Interruption Sensitivity Long interruption acceptable Short or No interruption acceptable Long interruption acceptable Shedd able Power Demand < 630 KVA ≤ 1250 KVA ≤ 2500 KVA ≤ 2500KVA > 2500 KVA > 2500 KVA  (And Several Buildings) Any Configuration Of Electrical Distribution Architecture (Load side of Transformers) Radial Radial - Double Ended Ring Ring Shedd able Load Two-Pole  Configuration Two-Pole  Configuration  With Two  ½ MLVS And No Link - Interconnected Switchboards

 Fig (3): Configurations of Electrical Distribution Architecture (Load side of Transformers)

10- Disturbance sensitivity

 # characteristic Definition choice 10 Disturbance sensitivity The ability of a circuit to work correctly in presence of an electrical power disturbance. Low Sensitivity: disturbances in supply voltages have very little effect on operations. E.g.: heating device. Medium Sensitivity: Voltage disturbances cause a notable deterioration in operations. E.g.: motors, lighting. High Sensitivity: Voltage disturbances can cause operation stoppages or even the deterioration of the supplied equipment. E.g.: IT equipment.

Types of disturbances with an impact on circuit operations:

1. Brown-outs,
2. Over voltages,
3. Voltage distortion,
4. Voltage fluctuation,
5. Voltage imbalance.
A disturbance can lead to varying degrees of malfunctioning. E.g.: stopping working, incorrect working, accelerated ageing, increase of losses, etc.

Effect of Disturbance sensitivity value on Configuration of Electrical Distribution Architecture:

The sensitivity of circuits to disturbances determines the design of shared or dedicated power circuits. Indeed it is better to separate “sensitive” loads from “disturbing” loads. E.g.: separating lighting circuits from motor supply circuits. This choice also depends on operating features. E.g.: separate power supply of lighting circuits to enable measurement of power consumption.

And the following table summarizes the suitable Disturbance sensitivity value for different Configurations of Electrical Distribution Architecture (Load side of Transformers)( see fig.3):

 Disturbance sensitivity value Low Sensitivity High Sensitivity Configuration Of Electrical Distribution Architecture (Load side of Transformers) Radial Sheddable Load Two-Pole Interconnected Switchboards Ring Double Ended

11- Disturbance capability of circuits

 # Characteristic Definition Choice 11 Disturbance capability of circuits The ability of a circuit to disturb the operation of surrounding circuits due to phenomena such as: harmonics, in-rush current, imbalance, High Frequency currents, electromagnetic radiation, etc. Non Disturbing Moderate Or Occasional Disturbance Very disturbing

This characteristic is related to the above characteristic “Disturbance sensitivity” for far extent and they must be studied together for obtaining an optimal Configuration of Electrical Distribution Architecture.

The following table summarizes the effect of Disturbance capability of circuits on Configuration of Electrical Distribution Architecture (Load side of Transformers)

 Disturbance Capability Of Circuits Value Non Disturbing Moderate Or Occasional Disturbance Very disturbing Action Taken For Configuration Of Electrical Distribution Architecture (Load Side Of Transformers) no specific precaution to take Separate power supply may be necessary in the presence of medium or high sensitivity circuits. E.g.: lighting circuit generating harmonic currents. A dedicated power circuit or ways of attenuating disturbances are essential for the correct functioning of the installation. E.g.: electrical motor with strong start-up current, welding equipment with fluctuating current.

In the next topic, I will continue explaining other Electrical installation characteristics and Technological characteristics. So, please keep following.