What is Fault Current?

You might notice that breaker (or MCCB) always denote with the “KA” value. But what is KA actually?

KA is the amperage value (in Kilo Amp) for the fault current.

Fault current, also called "short-circuit current" (I_SC) (and sometimes called symmetrical fault current) describes current flow during a short.

It passes through all components in the affected circuit. Fault current is generally very large and, therefore, hazardous which due to "fault condition" caused by the low-impedance, phase-to-phase or phase-to-ground connection.

The electrical distribution system should be designed to minimize the effect of a fault. When we experience a fault on an electrical system, the protection equipment will detect the fault and trip out the faulty circuit. It cannot however trip instantaneously, and a delay, (of up to a few seconds) will occur.

In a simple word, it prevents a short at an outlet from shutting down power to the entire building!

The formula for the short circuit current (I_SC) withstand capability of an electric cable is:

Where:
Isc = Short circuit rating of cable (kA)
A = Area of conductor (mm²)
t = Time to trip (in seconds)
K = 96 for PVC, Copper conductor
    = 62 for PVC, Aluminium conductor
    = 116 for PAPER, Copper conductor
    = 78 for PAPER, Aluminium conductor
    = 143 for XLPE, Copper conductor
    = 98 XLPE, Aluminium conductor

Example: For a 70mm², PVC insulated Copper conductor, the 1 second short circuit rating is:

Isc= (96 X 70) / sqrt 1 = 6.72KA

If the protection is fast, (say 0.2 seconds) then the conductor will have a 0.2 second short circuit rating of:

Isc= (96 X 70) / sqrt 0.2 = 15KA

Transfering The Electrical Load

One of my projects (for some reasons, the name of the project will not be revealed) is to design the electrical systems for commercial development. The scope of work is including the High Tension (HT) systems, Low Voltage (LV) systems and Extra Low Voltage (ELV).

In general, the development consists of two (2) blocks (A and B) with six floors for tenanted office and both blocks belongs to single owner.

The Owner having the intention to transfer the load for the tenanted area which initially taking the power supply from our local power utility provider Tenaga Nasional Behad (TNB) to the management (Landlord) supply.

The reason why the idea came across is that; there is a believing that the tariff that being imposed to the user is already caters for the maintenance charges, the modification works that needs to be done by the utility provider and all the cost incurred which due to the power that being supplied.

Considering that the maintenance and modification works happens  only once in the blue moon, the load rather to be parked in the management side than the utility provider. So... indirectly, the Owner no need to pay for all the extra charges and all the cost incurred instead borne by the utility provider...now will be under the Owner’s responsibilities.   

As a Consultant, we are instructed to do the study on the impact in term of technical and financially matters due to the transferring of these load.

Please take note that the rate and the currency might be differ to certain country as this study are based on Malaysian currency and TNB’s electricity tariff. Furthermore, this study should only to be taken as a reference and not to be taken as a solid proof.

The report are as per below:

The Study Of Transferring The Load

The objective of our study is to evaluate on the intention of the Owner to transferring the Tenant’s load for Block A to the Landlord’s load and to provide recommendation to the Client after completing of our study.

The evaluation shall be based on few parameters as per listed below:-

a)   Design Criteria
b)   Electricity Tariff Calculation
c)   Submission to Authorities
d)   Modification Works
e)   Cost Implication

DESIGN CRITERIA
In overall, the electricity scheme had been designed to segregate the Landlord’s load to the Tenant’s load (see photo below). By segregating these loads the Landlord and Tenant will be billed differently as per their individual tariff.

Click here for the original schematic diagram before transferring the load.

Landlord’s load will be under tariff C1 while tenant’s load will be under tariff B. The tenant load has been designed based on the concept that it will be rented or leased out as such TNB meter has been designed for.

In order to transfer the Tenant’s load to the Landlord, the electricity scheme needs to be redesign by means of swinging the incoming supply before the TNB’s Check Meter (see the clouded area at photo below) and then tapping from landlord load busbar instead.

Click here for the new schematic diagram after transferring the load.

ELECTRICITY TARIFF CALCULATION
The electricity tariff for Tenants currently will be billed as per Tariff B. After transferring the Tenant’s load to the Landlord, the new tariff for Tenants will be based on Tariff C1.

Below is the calculation of the Tenant’s monthly bill. These calculations are based on parameters as per below:

Total Maximum Demand for 24 Tenants       = 466.63 kW
Total Day Usage / Month                                 = 30 days
Load Factor                                                      = 0.25
Working hour                                                    = 12 hours.

The Unit Rate is based on the latest electricity tariff by TNB.

The Unit Rate for Tariff B                                       = RM 0.408 (attachment 3)
The Unit Rate for Maximum Demand Tariff C1   = RM 24.60 (attachment 3)
The Unit Rate for kWh Tariff C1                            = RM 0.296 (attachment 3)

a) Tariff B
Monthly Bill (RM) = Maximum Demand (kW) X Working Hour X Load Factor X Days X Unit Rate (RM)
                            = 466.63 KW X 12 Hr X 0.25 X 30 days X RM0.408
                            = RM 17,134.65

b) Tariff C1
Maximum Demand per month (MD/Month) = Maximum Demand (kW) X Load Factor X Unit Rate(RM)
                                                                     = 466.63 KW X 0.25 X RM24.60
                                                                     = RM 2,868.77

Monthly kWh = Maximum Demand (kW) X Working Hour x Load Factor X Days X Unit Rate (RM)
                      = 466.63KW X 12 Hr x 0.25 X 30 days X RM0.296
                      = RM 12,431.00

Monthly Bill (RM)   = MD/Month + Monthly kWh
                             = 2,869.77 + 12,431.00
                             = RM 15,300.77

Difference (RM)     = Tariff B - Tariff C1
                               = RM17,134.65 – RM15,300.77
                              = RM 1,833.88

Based on the calculation above, it can be concluded that by transferring the Tenant load to the Landlord load, the Owner will pay RM 1,833.88 lesser for the monthly electricity bill if all tenant load transfer to landlord load.

SUBMISSION TO AUTHORITIES
In order to transfer the Tenant’s load to the Landlord, the Consultant needs to submit the revised Single Line Diagram to TNB Metering and TNB Planner.

Transferring the load may affect the installation of TNB’s Check Meter. This Check Meter is monitoring the usage of all tenants including power consume by Food Court, Street Lighting, Sewerage Treatment Plant and others that parked under office load.

The decision on transferring the load should be finalized before installation of Check Meter take place. This is crucial as the Current Transformer (CT) for Check Meter need to be size-up based on the total load consumed.

MODIFICATION WORKS
Due to the transferring of the load, modifications need to be done to the Main Switch Board and an extra cable length required for swinging the power supply input.

The estimated time frame for this modification works will subject to the switch board manufacture and the availability of the cable in a market.

COST IMPLICATION
Additional costs are needed in transferring the load such as the cost to modify the Main Sub Board (MSB) and extra cost for connection fee in lieu of the additional Maximum Demand (MD).

The additional cost for modifying the MSB will be RM 40,000.00.

The total Maximum Demand for 24 nos. of Tenants is 466.63 kW and the rate for Connection Fee is based on RM 45.00 / kW. Therefore, the additional Connection Fee will be RM 20,998.35.

Adding these costs, the total additional cost required for transferring the load is totaling to RM 60,998.35.

However, by increasing the Maximum Demand of the power supply to the Landlord, the Owner should pay and additional meter deposit. Since the meter deposit is actually refundable therefore, we are not taking into account of this additional cost.

CONCLUSION
Based on the above evaluation, the Owner will have electricity bill saving of  RM 1,833.88 for the monthly bill and an extra cost of RM 60,998.35 for transferring the load.

The pay back period with saving of RM1,833.88 over the installation cost and contribution charges will be 33.26 months or 2.77 years.

If you consider the electricity tariff that being charged to the user is already cater for the maintenance charges by the utility provider, the cost incurred in the event of replacement of equipments needed and the cost of maintaining the power factor from the source of power supply. Then, the transferring the load is a wise decision and worth the money for Client to implement it.

Power Consume and Electricity Bill for Dimming and Non-Dimming Ballast for Street Lighting System

In one of my projects which due to the cost saving, the Owner having an intention to use the dimming ballast for their street lighting system.

I've been asked to come-up with a report on the cost saving that the Owner will get also to calculate the payback time using the dimming ballast system.

Below is my report;

Objective

The objective of this report is to tabulate the total power consumes and the electricity bill for dimming and non-dimming ballast for the Street Lighting System.

The calculation of the electricity bill will be divided into two segments, which is;

a) Calculation based on non-dimming ballast

b) Calculation based on dimming ballast

The parameters that being used in calculating the estimated MD will be as follows:

a)    Total power consume for street lighting system.

The total power consumed will be divided into two, which is non-dimming and

dimming system.

Total Power For Non-Dimming Ballast

i) (Operating Hour: 7pm-7am)

ID	DESCRIPTION	QTY	WATTAGE	TOTAL
1	250W & 150W (8m&6m Pole)	20	400	8,000.00
2	150W (8m Pole)	46	150	6,900.00
3	70W (4m Pole)	26	70	1,820.00
TOTAL WATTAGE				16,720.00

Total Power For Dimming Ballast

ii) (Operating Hour: 7pm-12m/night)

ID	DESCRIPTION	QTY	WATTAGE	TOTAL
1	250W & 150W (8m&6m Pole)	20	400	8,000.00
2	150W (8m Pole)	46	150	6,900.00
3	70W (4m Pole)	26	70	1,820.00
TOTAL WATTAGE				16,720.00

iii) (Operating Hour: 12m/night-7am)

ID	DESCRIPTION	QTY	WATTAGE	TOTAL
1	250W & 150W (8m&6m Pole)	20	200	8,000.00
2	150W (8m Pole)	46	75	3,450.00
3	70W (4m Pole)	26	70	1,820.00
TOTAL WATTAGE				9,270.00

Note:

1) Dimming ballast only apply for lantern which more than 150Watts.

2) Lantern will be dimmed to 50% of its rated wattage. This perecentage will subject to Owner's preference since the dimming ballast is a pre-set dimming ballast.

Power Consume and Electricity Bill for Dimming and Non-Dimming Ballast for Street Lighting

System

b) Operating hour

The operating hour for non-dimming and dimming system will be as per figure

below;

c) Unit rate based on tariff C1

The unit rate is based on latest TNB’s unit rate of RM0.288/kW.

Electricity Tariff Calculation

The whole development will be billed as per tariff C1. Based on tariff C1, the monthly

bill will be as per formula below:

Monthly Bill (RM) = MD/Month + Monthly kWh

Since the street lighting is only a small part from the total maximum demand consumed therefore, the MD/Month can be assumed constant and not into consideration for this calculation.

a) Calculation based on non-dimming ballast

Monthly kWh will be as per below:

Monthly kWh = Total Power (kW) X Working Hour X Load Factor X Days X Unit Rate (RM)

= 16.72kW X 12 Hr X 1 X 30 days X RM0.288

= RM 1,733.53

b) Calculation based on dimming ballast

Monthly kWh will be as per below:

Operating hour (7pm – 12m/night)

Monthly kWh = Total Power (kW) X Working Hour X Load Factor X Days X Unit Rate (RM)

= 16.72kW X 5 Hr X 1 X 30 days X RM0.288

= RM 722.30

Operating hour (12m/night – 7am)

Monthly kWh = Total Power (kW) X Working Hour X Load Factor X Days

X Unit Rate (RM)

= 9.27kW X 7 Hr X 1 X 30 days X RM0.288

= RM 560.65

Monthly Bill (RM) = Operating hour (7pm – 12m/night) + (12m/night – 7am)

= 722.30 + 560.65

= RM 1,282.95

Difference (RM) = non-dimming - dimming

= RM1,733.53 – RM1,282.95

= RM 450.58

Based on the calculation above, it can be concluded that by using the dimming ballast the monthly electricity bill can be reduce up to RM 450.58/month.

The budgetary cost for dimming ballast to be installed is RM 10.920.00. Therefore, the

Return on Investment for this dimming ballast system is within 24 months.

How To Design Capacitor Bank

It is crucial for electrical engineer to know on how to design the capacitor bank. The purpose of installing the capacitor bank is to counter the resistive load (KVAR) in the electrical system. By doing so, the power factor can be maintain to your required value and not to mentioned, it will save you lots of dollars as well as few more advantages by maintaining the power factor.

The Simple Way In Designing The Capacitor Bank

The simple way in designing the capacitor bank is by using the ready-made software. Just click here to download this software (in Excel format).

You would see the file as below once you open the file.

The above calculation is to design the required capacitor bank for Main Switchboard No.1. All the parameters such as transformer size and voltage are based on my total load for Main Switchboard No.1. You can simply change those values according to your own loads.

How The Software Works?

This software is will automatically calculated the required capacitor bank for your system once you key-in the values inside those cells. First and foremost, you need to determine the parameters below 

a)      Transformer Size

b)      The Secondary Voltage (it might be 400V or 415V)

c)       The Loading Factor of the transformer

d)      The Maximum Demand (MD)

e)      The Uncorrected Power Factor (PF)

f)       The Targeted Power Factor that you want to achieve

g)      The Main Voltage of your system (400V or 415V)

h)      The Capacitor Voltage

i)        The Filtering Factor

j)        The Frequency of the electrical system (50hz or 60hz) and

k)      The No. of steps for capacitor bank

Once you determine the parameters, what you’ll need to do is to key-in those parameters inside those cells as indicates in the figure below.

Then, you’ll see that, the value required for your capacitor bank is automatically calculated.

Based on the figure above, the required capacitor bank is 536.42kVAr. Therefore, the value of the capacitor bank shall be slightly higher than the calculated kVAr value. For this calculation I’m using the kVAr value of 550kVAr. This is due to the total kVAr value is based on the ratio of 25kVAr.

Instead of 25kVAr, there are few selections of kVAr ratio that can be use;

Until this stage, you already knew your required kVAr value, the number of steps and you have done selection of kVAr ratio that will be use in designing the capacitor bank. The next step is to determine the selection of power ratio. Figure below is a few selection of power ration that can be used.

In this calculation, I’m using the power ratio #3. Since the capacitor bank is designed according to 8 numbers of steps. Therefore, the selectable power ratio will follow the sequence below;

The selection of the power sequence depending on your selection of kVAr unit and the total kVAr needed to achieve the targeted power factor. Once the power ratio and the actual kVAr finalized, then key-in those values into the respective cells as per shown below.

Finally, you have completed designing your capacitor bank. Looking into the figure below, the actual kVAr is 550kVAr compared to the calculated kVAr of 536.42kVAr.

The minimum breaker rating for the capacitor bank is 771.15 Amp. Therefore, the nearest breaker rating that can be selected is 800Amp. The selection of the Current transformer (CT) is 1500/5A based on the Maximum Demand of 900kW and the c/k value will be 0.051.

[c/k value = Value of the reactive current response threshold of the Controller in Ar (ampere reactif)]