The Siam Photon Source is a 1 GeV electron storage ring for a synchrotron light source, now under test commissioning in Nakhon Ratchasima, Thailand. The bending magnets of the storage ring produce synchrotron light with photon energy usable up to the soft x-rays regions. In order to extend the usable photon spectrum to higher photon energies an insertion device with high magnetic field has to be installed into the storage ring. This report presents studies of perturbations from the magnetic field of such a device on the electron beam dynamics in the storage ring of the Siam Photon Source. The magnetic field of the device is simulated from arrays of permanent magnets. Random errors of the magnetic structure are included to take into account imperfection of a real device. Effects of perturbations from the magnetic field of the device on the electron beam dynamics are calculated. Possibilities to compensate the perturbations are investigated.