T H E S E - TEL

Potentiel d’économies d’énergie par les services énergétiques – Application au cycle de vie
des équipements de conversion de l’énergie
Annexe 2 : Exemple de contrat de performance
énergétique sous mécanisme « Guaranteed Savings » –
Exploitation et maintenance d’un automate de gestion
énergétique
Galva Plus is specialized in the hot galvanization of steel parts (barriers...). The main
equipment that needs electricity is an induction furnace used to maintain the Zinc in fusion
(450 °C). The latter is operating 24 h/24 and is on/off controlled: when the temperature of the
Zinc bath passes below the set point, the furnace is commanded to heat with full power
independently of the difference to this reference value. This kind of control thus does not
allow to manage the amplitude of the power demand and can generate important peaks. On
the other hand, when the furnace is off, the power demand of the site is low. In the framework
of an approach initiated by EDF, LM Control intervenes on site in order to optimize power
calls.
The invoicing of Electricity in France
The invoicing of EDF is based on two criteria: on the one hand a subscribed power and on the
other hand a price per kilowatt-hour consumed. The knowledge of consumption of the site
allows to optimize tariffs by balancing the subscribed power and the possible overstepping.
The subscribed power is then slightly lower than the total power absorbed. In spite of
optimization, EDF is conscious that it is possible to more decrease the subscribed power and
then to reduce the invoice of electricity. Indeed, EDF invoices its customers compared to their
load diagram which is established by averaging the power called over ten minutes. By
reducing the amplitude of power calls, it is possible to reduce the subscribed power and thus
the invoice.
The energy management system
Before the energy management device is set up, each process could call power at the same
time so that important peaks appeared on the load diagram. The client was then obliged to
subscribe a electricity supply contract in relation to the amplitude of these peaks.
This device allows to manage power calls. Indeed, when the power called passes over the set
point, the device switch the supply of certain equipments off. Also, when the power called
passes below the set point, the device switch the supply of certain equipments on. The on/off
priority depends on the process and the customer choices. Finally, load management with this
device is possible only for equipments with inertia and is then favorable for thermal uses
(furnace, cold group, …).
The specificity of the Galva Plus optimizer is that it manages only the furnace. LM Control
implements a power set point into the optimizer and synchronizes its clock with the EDF
network. In a 10 minutes interval, the optimizer calculates in real time the average power and
avoids exceeding the power set point by ordering the stop of the heat sequence even if the
Zinc bath did not reach the reference temperature. At the beginning of the next 10 minutes
interval, the optimizer restores the signal to the furnace and proceeds in the same way until
the reference temperature is reached.
207