Selective Coordination Tools and Spreadsheets - Part Two


In the prevouis Topic "Selective Coordination Tools and Spreadsheets - Part One", 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 previous Topic, we covered part one, part two and the first method of performing a selectivity coordination study By using Selective Coordination Time - Current Curves.

today, I will continue explaining other Methods of performing a selectivity coordination study as follows:


Second method: By using Selective Coordination Charts/Tables



1- What are the 
Selective Trip Coordination Charts/Tables?

Siemens  Selective Trip Coordination Charts/Tables   


ABB Selective Trip Coordination Charts/Tables 


GE Selective Trip Coordination Charts/Tables 
Selective Trip Coordination Charts/Tables are available which list, in varying styles as shown in pictures above for different manufacturers, breakers that selectively coordinate with other breakers at specific available fault current levels.

2- Comparison between selective coordination done by Time-Current Curves and that doing by Charts?

Time-Current Curves VS Charts

An advantage of the charts is that they are often more accurate than curve comparisons as they are based on more specific test data derived for selective coordination. If there is disagreement between overlaid curves and charts, the chart data should be used. 

3- How to Use  Selective Trip Coordination Charts/Tables 

The following Two steps will assure the best use of the Selective Trip Coordination Chart/Table for Siemens as example for other Manufacturers:
 

Siemens  Selective Trip Coordination Charts/Tables   
1. Conduct a short circuit study to determine the available fault current values at each level of the system where coordination is critical by using the Estimated Available Fault Current Calculator or any other Tool/Software.

2. Trip coordination is assured up to the value shown in the “Branch Coordination Level” column. A, short circuit study will be the best source of the maximum available fault current to be compared to the current value shown in this field.
Selective trip coordination is assured where the maximum available fault current value is less than this “Branch Coordination Level”. Faults occurring at the maximum calculated values are very rare so this is a conservative approach. The system designer may elect to consider other factors to balance the needs of system protection and coordination at various anticipated levels of current.



4- Important Notes for 
Siemens  Selective Trip Coordination Charts/Tables

a- In many cases the minimum frame MCCB will only coordinate at relatively low levels of fault current. If the level of selective coordination between the two circuit breakers initially selected is insufficient for the available fault current at that point in the system, the tables may be used to find an alternate upstream circuit breaker that will allow a higher level of coordination. This will usually involve a larger frame size or different type of circuit breaker such as an insulated case or power breaker. The table is ordered from lower to higher coordination current levels so that by moving down the table it is possible to find an upstream breaker that will deliver a higher level of selective coordination.

b- Coordination is assured up to the value of current shown in the "Branch Coordination Level" field.

c- If the available fault current at the branch is unknown, the distribution transformer let-through value will provide a conservative available fault current for this use. The published data for the transformer should be consulted. Coordination is assured when the available fault current at the main is less than or equal to the value shown in the "Branch Coordination Level" field.

d- If the main breaker has an Instantaneous setting it must be set at maximum, branch Instantaneous must be set below “Branch Coordination Level” including bandwidth tolerances.

e- Coordination in the thermal range is also achieved, including instances where the tolerance bands touch but do not overlap. Electronic trip units must be adjusted for Long Time and Instantaneous functions (also Short Time if so equipped). As shipped, factory settings are minimum. Electronic trip mains must be adjusted to near maximums, standard trip curve coordination overlay techniques may be used for exact settings.

f- Applicable voltage range is marked for each chart.

g- Breaker types shown in the table except as shown below, consult literature for voltage and AIC ratings:

(ED) includes the following types: ED4, ED6, HED4, and CED6
(FD) includes the following types: FXD6-A, FD6-A, FD6, HFD6, HFXD6, and CFD6
(JD) includes the following types: JXD2-A, JXD6-A, JD6-A, JD6, JXD6, HJD6-A, HJD6, HJXD6-A, HJXD6, and CJD6-A
(LD) includes the following types: LXD6-A, LD6-A, LD6, LXD6, HLXD6-A, HLD6-A, HLD6, HLXD6, and CLD6-A
(LMD) includes the following types: LMD6, LMXD6, HLMD6, and HLMXD6
(MD) includes the following types: MD6, MXD6, HMD6, HMXD6, and CMD6
(VL) family circuit breakers include interrupting ratings up to the maximum for each frame.
(VL -FG) applies to NFG, HFG, and LFG types. If there is no trip unit reference all types apply, i.e. 525, 545, and 576. If electronic only applies it is so noted, i.e. NG-545, and also applies to NG-576 electronic.

h- The Siemens ‘SBS’ frame circuit breaker is no longer available for new construction and is included only for existing installations. The replacement for this frame is the ‘WL’ frame circuit breaker.


To download a copy of Siemens selectivity coordination tables, please click the link.


In the next Topic, I will explain The third method for performing 
a selectivity coordination study  By using Siemens calculators / spreadsheets. please, keep following.


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