Selective Coordination Tools and Spreadsheets - Part Three



In the previous Two Topic "Selective Coordination Tools and Spreadsheets - Part One" and "Selective Coordination Tools and Spreadsheets - Part Two", I showed that our study for selective Coordination will be based on the following main parts:

Part One: What is selective coordination?

Part Two: NEC code and Selective Coordination

Part Three: Method of performing a selectivity coordination study

  • First: By using Selective Coordination Time - Current Curves
  • Second: By using Selective Coordination Charts/Tables.
  • Third: By using Siemens calculators / spreadsheets.

in this Two previous Topic, we covered part one, part two and the first Two methods of performing a selectivity coordination study By using Selective Coordination Time - Current Curves & by using 
Selective Coordination Charts/Tables .

today, I will continue explaining the third Method of performing a selectivity coordination study as follows:

Third: By using Siemens Calculators / Spreadsheets


An excellent spreadsheet provided by Siemens includes two different calculators as follows:
  1. Siemens Estimated Available Fault Current Calculator.
  2. Siemens Selective Coordination Tool.

This spreadsheet allows using of the selective coordination Tool in addition to the estimated Available Fault Current Calculator by following the next steps to get more reliable selections of overcurrent devices. 

First: Siemens Estimated Available Fault Current Calculator

Siemens Estimated Available Fault Current Calculator
In a previous topic, I explain in detail the Method of using Siemens Estimated Available Fault Current Calculatorhow to enter the input data to get the required output data.


Second: Selective Coordination Tool


Siemens has developed this Selective Coordination Tool to assist in designing code compliant systems.

Selective Coordination Tool
This tool includes three worksheets as follows: 
  1. Selective coordination tool worksheet.
  2. Selective coordination Info worksheet.
  3. Selective coordination Hints worksheet.

Selective Coordination Tool using manual:


First: Selective coordination tool worksheet


The above Drawing is a generic one-line that can be used for many different configurations. The labels (MDP), (DP) and (LP) are to identify three available fault current locations.

We will use this tool to identify breaker pairs that coordinated to a given available fault current (AFC). To meet the requirements of selective coordination, BRANCH and CB3 must coordinate to the AFC at LP , CB3 and CB2 must coordinate at the AFC at LP, CB2 and CB1 must coordinate to the AFC at DP, and CB1 and MAIN must coordinate to the AFC at MDP (the downstream device determines the level of coordination).

Fig (1)
1- In fig (1), Provide the voltage for the breakers being evaluated – use 240 for a 208 V system (put 240V for ex.) 

Fig (2)
2- In fig (2), Select the branch circuit breaker type that you intend to use as overcurrent device for this branch circuit, from the drop down box beside BRANCH word (select BQD20 for ex.) 

Notes:
A- Only the white fields are user inputs.

B- Always pull down the list to see your choices – sometimes the smallest is not displayed first.

C- The breakers shown are the type, not the specific breaker. For Example: FD 250 indicates a type FD with a 250A trip. This breaker type is available in four AIC rating models, the FD6 (35/35 KAIC at 240/480V), the HFD6 (100/65 KAIC), the HHFD6 (200/100 KAIC), and the CFD6 (200/200 KAIC)- refer to the
SpeedFax Product Catalog for the correct circuit breaker. Make sure you specify the correct version or required AIC level in the specifications or by schedule.

D- An (s) designation after the breaker type (ex. SMD 800 s) indicates a solid state electronic trip circuit breaker. No (s) indicates a thermal-magnetic trip circuit breaker. All type (WL) breakers are solid state.

E- The UL 489 and UL 1066 notations for the type (WL) insulated case breaker indicate switchboard application or switchgear application, respectively. The (FS) notation indicates the frame size.


3- By using Estimated Available Fault Current Calculator, Determine the available fault currents for Panel (LP) in fig (1) at the incoming location and put the value (say it will be 900A for ex.) in the White Cell beside (LP) alphabets.

Note:

you will have to recalculate available fault currents and recheck the breaker pairs each time you increase the conductor size after using the Estimated Available Fault Current Calculator. The fault current calculator makes this easy.

4- From the drop down box beside CB3 in fig(2) , choose the smallest circuit breaker type that has an instantaneous trip larger than 900A (including the tolerance band), you will find each breaker instantaneous trip value in the box beside the chosen type under The (Coordinates To) field.( select ED120 for ex. You will find that its smallest instantaneous trip is 1000A which is larger than 900A fault current in the downstream branch circuit of CB BQD20, this means that the CB Pairs – BQD20 & ED120- will selectively coordinate with each other).

Note
The (Coordinates To) field indicates the heist level of fault current (in amps) to which the shown breaker pair will selectively coordinate.

5- Repeat step #3 to get the available fault currents for the incoming location of Panel (DP) and put it in the white cell beside the (DP) alphabets (say it will be 2500A for ex.)

6- Repeat step #4 but for CB2 and note that the selected CB type must has smallest instantaneous trip value larger than 2500A ( select SJD300 s) with instantaneous trip value 3100A. So, CB pairs ED120 & SJD300 s will selectively coordinate with each other.

7- It is become easy now to repeat step #3 for main distribution panel (MDP)(say it will be 9000A for ex.)

8- Also, it is easy now to repeat step #4 for CB1, the result will be breaker type SMD800 s with 9600A with instantaneous trip value. So, CB pairs SJD300 s & SMD800 s will selectively coordinate with each other

9- repeat step #4 for Main CB which must has instantaneous trip value larger than that of CB1 and for our example we select breaker SND1200 s with 10000A instantaneous trip value . So, CB pairs SMD800 s & SND1200 s will selectively coordinate with each other

Note:You may not always have a breaker that corresponds to CB1, CB2 and CB3. If that is the case, select (none) from the available breaker pull down list. For example, if you have a 20A branch (BRANCH) in a MLO panel (LP) fed from a feeder breaker (CB1) in (MDP), you may select (none) for CB3 and CB2. BRANCH will then coordinate with CB1 to the AFC (Available Fault Current) at (LP), and CB1 will coordinate with MAIN to the AFC at (MDP).


In case of using Emergency Generators as an Electrical Source:

fig (3): Generator Fault Current Calculator
When the system is being powered by the emergency source, the coordination must now be calculated based on the new available fault current.

1- put the generator KW.

2- put the output voltage in Volts ( only for 3 phase)

3- find the sub-transient impedance (X”d) for your generator from the generator manufacturer – this must be a per unit value and put it in the white cell beside the (X”d per unit) words.

4- You will get the Generator fault current value in Amps.

5- Insert the Gen Fault current Value into (or secondary available fault current) field in the Estimated Available Fault Current Calculator and put other data for distance, conductor material, method of installation and conductor shield material, so you will get the Fault Current Available in Amps incoming location of panel (LP).

6- From the drop down box beside CB3 in fig (2) , choose the smallest circuit breaker type that has an instantaneous trip larger than Fault Current Available gotten from step #5, to ensure that the CB Pairs – CB3 & BRANCH - will selectively coordinate with each other.

7- From the drop down box beside GEN 
in fig (2), choose the smallest circuit breaker type that has an instantaneous trip larger than that of CB3 gotten from step #6, to ensure that the CB Pairs – CB3 & Generator - will selectively coordinate with each other. 

General notes:


a- The Siemens selective coordination tool will identify commonly used Siemens circuit breaker whose trip curves do not overlap for the conditions selected by the engineer. The tool will identify coordinated commonly used breaker pairs for up to five levels of distribution. In some cases, Siemens has additional devices and solutions available for especially difficult design conditions.

b- The Siemens selective coordination tool is based on data for Siemens circuit breakers that may or may not be similar to products by other manufacturers. Siemens suggest noting on the panel schedule the Siemens breaker suggested by the tool and calling for an equivalent product for other approved manufacturers. Inclusion of the Siemens breaker type and size will provide some of the information needed to select the alternate product.

c- The choice of selectively coordinated devices requires calculation (and frequently recalculation) by the engineer of the available fault current at various points in the system, and often requires resizing panels, switchboards, conductors, conduits and other system components. This redesign cannot be done during the bidding process, and can be extremely costly if done during construction. For this reason, the engineer is responsible for selecting and calling for the correct selectively coordinated devices.

Second & Third: Selective coordination Info & Hints worksheets

Selective coordination Info & Hints worksheets    


These worksheets will act as a simple user guide which include steps and tips for using selective coordination tool worksheet.


To download your copy from
 Siemens Estimated Available Fault Current Calculator + Selective Coordination Tool , please Right click on the link and choose save as.




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