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Calculating Shrinkage

Use the following formulae and examples to calculate shrinkage on Pacific Gas and Electric Company's gas pipeline system. In each formula:


X = the decimal equivalent of the transmission shrinkage percentage
Y = the decimal equivalent of the distribution shrinkage percentage
Z = the decimal equivalent of the storage injection shrinkage percentage

Examples on this page are for demonstration purposes only, and use the shrinkage factors effective May 1, 2004.

Transmission Shrinkage

Use these formulae to calculate shrinkage when moving gas to the Citygate, to an off-system destination or to a transmission-level noncore end-use customer

Calculating Receipt Point Volumes from Delivery Point Volumes

When entering nominations using delivery point volumes, the formula to determine receipt point volumes is:

receipt point volume = delivery point volume / (1-X)


For example, if you want 700 Dth delivered to the Citygate, you will need 709 Dth at an interconnect receipt point such as Topock or Malin.

receipt point volume = 700 Dth / (1-0.012) = 709 Dth


Note: When calculating receipt point volumes from delivery point volumes, INSIDEtracc always rounds up to the next highest integer. In this case, 708.502 Dth rounds up to 709 Dth.

Calculating Delivery Point Volumes from Receipt Point Volumes

When entering nominations using receipt point volumes, the formula to determine delivery point volumes is:


delivery point volume = receipt point volume * (1-X)


For example, to calculate the volumes delivered from a receipt point volume of 709 Dth:


delivery point volume = 709 Dth * (1-0.012) = 700 Dth


Note: When calculating delivery point volumes from receipt point volumes, INSIDEtracc always rounds down to the next integer. In this case, 700.492 Dth rounds up to 700 Dth.

Distribution Shrinkage

Use these formulae to calculate shrinkage to end-use customers on Pacific Gas and Electric Company's distribution system.

Calculating Receipt Point Volumes from Estimated Metered Usage

To calculate the receipt point volumes required to supply a given burner tip volume, use the following formula:


receipt point volume = estimated metered usage * (1+Y) / (1-X)


For example, if you want 700 Dth delivered to a distribution-level noncore customer, you will need 710 Dth at an interconnect receipt point such as Topock or Malin.


receipt point volume = 700 Dth * (1+0.002) / (1-0.012) = 710 Dth


Note: When calculating receipt point volumes from usage, INSIDEtracc always rounds up to the next integer. In this case, 709.919 Dth rounds up to 710 Dth.

Calculating Estimated Metered Usage from Receipt Point Volumes

To determine burner tip volumes from a given receipt point quantity, use the following formula:


estimated metered usage = receipt point volume * (1-X) / (1+Y)


For example, to calculate the volumes delivered to a distribution-level noncore end-use customer from 710 Dth at an interconnect receipt point such as Topock or Malin:


estimated metered usage = 710 Dth * (1-0.012) / (1+0.002) = 700 Dth


Note: When calculating usage from receipt point volumes, INSIDEtracc always rounds down to the next integer. In this case, 700.080 Dth becomes 700 Dth

Storage Injection Shrinkage

Use these formulae to calculate shrinkage when injecting gas into a California Gas Transmission storage account.

Calculating Citygate Receipt Point Volumes from Volumes Delivered into Storage

If you know the volume of gas that you would like delivered into your storage account, use the following equation to determine how much gas you will need at the Citygate:


receipt point volume = delivered volume / (1-Z)


For example, you must nominate 1,009 Dth from a Citygate pool to deliver 1,000 Dth into a CGT storage account.


receipt point volume = 1,000 Dth / (1-0.008) = 1,009 Dth


Note: When calculating receipt point volumes from delivery point volumes, INSIDEtracc always rounds up to the next integer. In this example, 1,008.065 Dth rounds up to 1,009 Dth

Calculating Volumes Delivered into Storage from Citygate Receipt Point Volumes

Calculating Volumes Delivered into Storage from Citygate Receipt Point Volumes If you know the volume of gas at a Citygate receipt point, use the following equation to determine how much gas you will deliver into storage after applying in-kind shrinkage:


delivered volume = receipt point volume * (1-Z)


For example, if you nominate 1,009 Dth at the Citygate into your storage account, volumes injected into storage will be 1,000 Dth.


delivered volume = 1,009 Dth * (1-0.008) = 1,000 Dth


Note: When calculating delivery point volumes from receipt point volumes, INSIDEtracc always rounds down to the next integer. In this example, 1,000.928 Dth rounds down to 1,000 Dth

Calculating Receipt Point Volumes at an Interconnect from Volumes Delivered into Storage

If you know the volume of gas that you would like delivered into your storage account, use the following equation to determine how much gas you will need at an interconnect receipt point:


receipt point volume = (delivered volume) / [ (1-Z) * (1-X) ]


For example, you must nominate 1,021 Dth from a Topock interconnect receipt pool to deliver 1,000 Dth into a CGT storage account.


receipt volume = (1,000 Dth) / [ (1-0.008) * (1-0.012) ] = 1,021 Dth


Note: When calculating receipt point volumes from delivery point volumes, INSIDEtracc always rounds up. In this example, 1,020.308 Dth becomes 1,021 Dth

Calculating Volumes Delivered into Storage from Receipt Point Volumes at an Interconnect

If you know the volume of gas at an interconnect receipt point, use the following equation to determine how much gas you will deliver into storage after applying in-kind shrinkage:


delivered volume = (receipt point volume) * (1-Z) * (1-X)


For example, if you nominate 1,021 Dth from a Topock receipt point into your storage account, 1,000 Dth will be injected.


delivered volume = (1,021 Dth) * (1-0.008) * (1-0.012) = 1,000 Dth


Note: When calculating delivery point volumes from receipt point volumes, INSIDEtracc always rounds down. In this example, 1,000.678 Dth becomes 1,000 Dth.

Two Noms Require Two Shrinkage Calculations

Because of the rounding rules utilized by INSIDEtracc, your storage shrinkage calculation must mimic your gas nomination with respect to the Citygate. That is, if your gas is nominated directly from an interconnect receipt point to a storage account, your shrinkage calculation should use the single storage injection shrinkage formula shown above.


delivered volume = (receipt point volume) * (1-Z) * (1-X)


However, if your storage gas is nominated using two separate nominations, the first from an interconnect to the Citygate and the second from the Citygate into storage, please be aware two separate calculations are required to accurately account for shrinkage gas. First, you should apply the transmission shrinkage formula above to determine volumes delivered to the Citygate from an interconnect receipt point.


delivery point volume = receipt point volume * (1-X)


Next, apply the storage shrinkage formula to determine volumes delivered into storage from the Citygate receipt point


delivered volume = (receipt point volume) * (1-Z).


Failure to follow this rule may lead to inaccurate accounting for INSIDEtracc's rounding, and your shrinkage calculation may be off by 1 Dth.

Injection MDQ

Storage injection MDQs apply to shrunk volumes

Additional Resources

If you have any questions about CGT's shrinkage factors or calculations, please contact your CGT Account Services Representative.