[016] - Programas demo do PLC S7-1200 da SIEMENS (Simatic)

Load management with S7-1200 and SENTRON PAC3200

Problem Power utilities charge industrial electricity customers not only for the active energy consumed (in kWh), but they also make the kilowatthour rate dependent on a power limit (in kW). The power limit is defined as the average of the total electric power imported over a defined measuring period. If this power limit specified by the power utility is exceeded, a higher kWh price will be charged for the entire accounting period (e.g., 1 month or 1 year, depending on the terms of the contract). To avoid this, large-scale electricity customers temporarily switch off dispensable loads. Now the task in this application is as follows :

Relative to the start of the respective measuring period, the total average power demand of all loads is to be permanently determined to forecast it for the end of the measuring period. If it is expected that the power limit will be exceeded, loads are to be temporarily switched off according to a priority list.

The respective total average power demands at the end of the measuring periods are to be logged over at least the accounting period to furnish proof to the power utility.

Solution For load control a SIMATIC CPU S7-1200 is used. SENTRON PAC3200 multi-function measuring instruments are used to measure the power or electrical energy of the loads. As the HMI a KTP600 operator panel is used.

The measured data at the power infeed point necessary for load control is acquired individually for each load by the SENTRON PAC3200 multi-function measuring instruments and added up in the PLC. The SENTRON PAC3200 devices transmit the data to the controller via "MODBUS on TCP". The switching-off of loads that is required when there is an imminent exceeding of the power limit is performed using the digital output of the relevant SENTRON PAC3200 device. The SENTRON PAC3200 devices receive the associated switching commands from the PLC via MODBUS communication.

Figure 01

The data logging is carried out with the S7-1200 data log function. At the end of the measuring period, the total average power demand relative to the measuring period is written to a csv-file in the load memory resp. to the memory card. Via the S7-1200 webserver you have access to the csv-file at any time.

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[016] - Programas demo do PLC S7-1200 da SIEMENS (Simatic)

Figure 02

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Documentation Load Management with S7-1200 and SENTRON PAC3200

Code STEP 7 project (SIMATIC STEP 7 BASIC V11 SP2, SIMATIC WINCC BASIC V11 SP2)

Last ChangesFirst edition

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Hardware platform: SENTRON, SIMATIC S7-1200

Software: STEP 7 since V11

Entry contents: Application Examples

Date: 2012-05-24

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[016] - Programas demo do PLC S7-1200 da SIEMENS (Simatic)

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